In English we use “should” verb to indicate the desired behavior.
e.g. “He should go to school”; “You should take medicine”; “They should not have done this”

In Marathi sentence formation is :

Form of हवे (have) are हवा-हवी-हवे-हवे-हव्या-हवी (havA-havI-have-have-havyA-havI) this follows आ-ई-ए-ए-या-ई (A-I-e-e-yA-I) rule

He should have eaten mango -> त्याने आंबा खायला पाहिजे/हवा होता (tyAne AMbA khAyalA pAhije/havA hotA)
He should have eaten tamarind -> त्याने चिंच खायला पाहिजे/हवी होती (tyAne chiMch khAyalA pAhije/havI hotI)

Generally, while speaking in the present tense form of असणे(“asaNe”) i.e. “आहे” is omitted.
He should eat mango -> त्याने आंबा खायला पाहिजे/हवा (tyAne AMbA khAyalA pAhije/havA hotA)
He should have eaten tamarind -> त्याने चिंच खायला पाहिजे/हवी(tyAne chiMch khAyalA pAhije/havI)

For अकर्मक (akarmak) verbs; the object is assumed to be of neuter-singular gender
He should go: – त्याने जायला पाहिजे (tyAne jAyalA pAhije)
He should have gone: – त्याने जायला पाहिजे होते (tyAne jAyalA pAhije hote)
I should speak:- मी बोलायला पाहिजे (mI bolAyalA pAhije)
I should have spoken:- मी बोलायला पाहिजे होते (mI bolAyalA pAhije hote )

By using नाही पाहिजे (nAhI pAhije ) we make the sentence negative. In negative sentences, we do not use the form of हवे(have).

They (plural of she) should dance: – त्यांनी नाचायला पाहिजे (tyAMnI nAchAyalA pAhije)
They (plural of she) should not dance:-त्यांनी नाचायला नाही पाहिजे (tyAMnI nAchAyalA nAhI pAhije )
They (plural of she) should have danced:- त्यांनी नाचायला पाहिजे होते (tyAMnI nAchAyalA pAhije hote)
They (plural of she) should not have danced:- त्यांनी नाचायला नाही पाहिजे होते (tyAMnI nAchAyalA nAhI pAhije hote)

In such sentences in the simple present tense; with You(singular); we can use पाहिजेस (pAhijes) instead of पाहिजे (pAhije).
In perfect tense sentences, we use only पाहिजे (pAhije) but extra स(s) is appended to form of असणे(“asaNe”)

You should play -> तू खेळायला पाहिजे/पाहिजेस (tU kheLAyalA pAhije/pAhijes)
You should smile -> तू हसायला पाहिजे/पाहिजेस -> (tU hasAyalA pAhije/pAhijes)
You should not play -> तू खेळायला नाही पाहिजे/पाहिजेस (tU kheLAyalA pAhije/pAhijes)
You should not smile-> तू हसायला नाही पाहिजे/पाहिजेस (tU hasAyalA pAhije/pAhijes)
You should have played -> तू खेळायला पाहिजे होतेस (tU kheLAyalA pAhije hotes )
You should not have smiled->तू हसायला नाही पाहिजे होतेस (tU hasAyalA nAhI pAhije hotes )

Another way of creating negative sentences is to use नको(nako) Instead of नाही पाहिजे (nAhI pAhije )

e.g.
They (plural of she) should not dance:-त्यांनी नाचायला नको (tyAMnI nAchAyalA nako)
They (plural of she) should not have danced:- त्यांनी नाचायला नको होते (tyAMnI nAchAyalA nako hote)
You(singular) should not have smiled -> तू हसायला नको होतेस (tU hasAyalA nako hotes )

In this style; पाहिजे(pAhije) is appended to corresponding sentences in simple past tense to indicate “should”. The example will make it clear. As verb form in simple past tense depends on verb type; I have grouped them separately

#1) For सकर्मक (sakarmak ) verbs i.e. verbs that need noun
He should eat mango -> (He ate mango) + पाहिजे (pAhije) -> त्याने आंबा खाल्ला पाहिजे (tyAne AMbA khAllA pAhije)
So, He should eat mango -> त्याने आंबा खाल्ला पाहिजे (tyAne AMbA khAllA pAhije)

Similarly other examples:-

She should open box -> (She opened box) + पाहिजे (pAhije) -> तीने पेटी उघडली पाहिजे (tIne peTI ughaDalI pAhije)
I should push you -> (I pushed you) + पाहिजे (pAhije) -> मी तुला ढकलले पाहिजे (mI tulA Dhakalale pAhije)
Monster should eat her -> (Monster ate her) + पाहिजे (pAhije) -> राक्षसाने तीला खाल्ले पाहिजे (rAkShasAne tIlA khAlle pAhije)
They should open box -> (They opened box) + पाहिजे (pAhije) -> त्यांनी पेटी उघडली पाहिजे (tyAMnI peTI ughaDalI pAhije)

#1a) If the noun is absent then it is assumed to be neuter singular.
He should eat -> (He ate) + पाहिजे (pAhije) -> त्याने खाल्ले पाहिजे (tyAne khAlle pAhije)
He should open -> (He opened) + पाहिजे (pAhije) -> त्याने उघडले पाहिजे (tyAne ughaDale pAhije)

#1b) If noun is plural then instead of पाहिजे (pAhije) we use पाहिजेत (pAhijet)
We should follow rules -> (We followed rules ) + पाहिजेत (pAhijet) -> आपण नियम पाळले पाहिजेत (ApaN niyam pALale pAhijet)
He should watch movies -> (He watched movies) + पाहिजेत (pAhijet) -> त्याने चित्रपट बघितले पाहिजेत(tyAne chitrapaT baghitale pAhijet)

#2) अकर्मक(akarmak) verbs i.e.verbs that do not need the noun
He should go -> (He went) + पाहिजे (pAhije) -> तो गेला पाहिजे (to gelA pAhije)
She should go -> (She went) + पाहिजे (pAhije) -> ती गेली पाहिजे (tI gelI pAhije)
I(male) should go -> (I went) + पाहिजे (pAhije) -> मी गेलो पाहिजे (mI gelo pAhije)

#2a) In case of अकर्मक(akarmak) verbs, for third person plural; instead of पाहिजे (pAhije) we use पाहिजेत (pAhijet)
They should speak -> They spoke + पाहिजेत (pAhijet) -> ते बोलले पाहिजेत (te bolale pAhijet)
They should cry -> They cried + पाहिजेत (pAhijet) -> ते रडले पाहिजेत (te bolale pAhijet)

#3) When creating such sentences with You(singular); then ending स(s) of the verb form is taken out and appended to पाहिजे (pAhije)

You(male) should go -> (You went) + पाहिजे (pAhije) -> तू गेलास(tU gelAs) + पाहिजे (pAhije) -> तू गेला पाहिजेस (tU gelA pAhije)
You(male) should eat mango -> (You ate mango) + पाहिजे (pAhije) -> तू आंबा खाल्लास (tU AMbA khAllAs) + पाहिजे (pAhije) -> तू आंबा खाल्ला पाहिजेस (tU AMbA khAllA pAhijes)

#4) When creating such sentences with You(plural); then ending त(t) of verb form is taken out and appended to पाहिजे (pAhije)
You(plu.) should go -> (You went) + पाहिजे (pAhije) -> तुम्ही गेलात (tumhI gelAt) + पाहिजे (pAhije) -> तुम्ही गेला पाहिजेत (tumhI gelA pAhijet)
You(plu.) should eat mango -> (You ate mango) + पाहिजे (pAhije) -> तुम्ही आंबा खाल्लात (tumhI AMbA khAllAt) + पाहिजे (pAhije) -> तुम्ही आंबा खाल्ला पाहिजेत (tumhI AMbA khAllA pAhijet)

#5) Special way Even for अकर्मक(akarmak) verbs, sentences can be formed as in सकर्मक (sakarmak ) verbs by creating neuter-singular form of verb
He should go -> त्याने गेले पाहिजे (tyAne gele pAhije)
She should go -> तीने गेले पाहिजे (tIne gele pAhije)
I should speak -> मी बोलले पाहिजे (tIne bolale pAhije)
They should cry -> त्यांनी रडले पाहिजे (tyAMnI raDale pAhije)

In such sentences we use पाहिजेस(pAhijes ) for You(singular)
You(sing.) should go -> तू गेले पाहिजेस (tyAne gele pAhijes)
You(sing.) should speak -> तू बोलले पाहिजेस (tIne bolale pAhijes)

#6) Past tense sentences can be formed by using पाहिजे (pAhije) along with in sentence in past perfect tense.
We just swap position of पाहिजे (pAhije) and form of असणे(“asaNe”)
We always use पाहिजे (pAhije) and never पाहिजेस(pAhijes) or पाहिजेत(pAhijet)

e.g.

He should have gone -> (He had gone ) + पाहिजे (pAhije) -> तो गेला होता (to gelA hotA) + पाहिजे (pAhije) -> तो गेला पाहिजे होता (to gelA pAhije hotA)
So, He should have gone -> तो गेला पाहिजे होता (to gelA pAhije hotA)

They should have cried -> (They had cried) + पाहिजे (pAhije) -> ते रडले होते (te bolale hote) + पाहिजे (pAhije) -> ते रडले पाहिजे होते (te bolale pAhijet hote)

Monster should have eaten her -> (Monster had eaten her) + पाहिजे (pAhije) -> राक्षसाने तीला खाल्ले होते(rAkShasAne tIlA khAlle hote) + पाहिजे (pAhije) -> राक्षसाने तीला खाल्ले पाहिजे होते(rAkShasAne tIlA khAlle pAhije hote).

They should have opened box -> (They had opened box) + पाहिजे (pAhije) -> त्यांनी पेटी उघडली (tyAMnI peTI ughaDalI ) + पाहिजे (pAhije) -> त्यांनी पेटी उघडली पाहिजे होती (tyAMnI peTI ughaDalI pAhije hotI)

You(sing.) should have followed rules -> (You(sing.) had followed rules ) + पाहिजे (pAhije) -> तू नियम पाळले होतेस (tU niyam pALale pAhije ) + पाहिजे (pAhije) -> तू नियम पाळले पाहिजे होतेस (tU niyam pALale pAhije hotes)

Same as style 1; instead of पाहिजे(pAhije) we use नाही पाहिजे(nAhI pAhije) to make sentences in negative

He should not go -> तो गेला नाही पाहिजे (to gelA nAhI pAhije)
She should not open box -> तीने पेटी उघडली नाही पाहिजे (tIne peTI ughaDalI nAhI pAhije)
He should not eat -> त्याने खाल्ले नाही पाहिजे (tyAne khAlle nAhI pAhije)
He should not watch movies -> त्याने चित्रपट बघितले नाही पाहिजेत(tyAne chitrapaT baghitale nAhI pAhijet)
They should not cry -> ते रडले नाही पाहिजेत (te bolale nAhI pAhijet)
You(plu.) should not eat mango -> तुम्ही आंबा खाल्ला नाही पाहिजेत (tumhI AMbA khAllA nAhI pAhijet)
You(sing.) should not have followed rules -> तू नियम पाळले नाही पाहिजे होतेस (tU niyam pALale nAhI pAhije hotes)

This is an older and more bookish way. You will find its many occurrences many times but less compared to the above way.
In Marathi sentence formation is :

To open: उघडणे (ughaDaNe) Forms will be
उघडावा – उघडावी -उघडावे -उघडावे -उघडाव्या -उघडावी (ughaDAvA-ughaDAvI-ughaDAve-ughaDAve-ughaDAvyA-ughaDAvI)

If verb already ends with sound आ(A) then we simply append
वा-वी-वे-वे-व्या-वी (vA-vI-ve-ve-vyA-vI)

To eat:- खाणे(khANe)
खावा-खावी-खावे-खावे-खाव्या-खावी (khAvA-khAvI-khAve-khAve-khAvyA-khAvI)

The form depends on gender and multiplicity of object
So for verb खाणे(khANe) if the object of is masculine-singular then verb form will be खावा (khAvA). If the object of is feminine-singular then verb form will be खावी (khAvI).

This follows आ-ई-ए-ए-या-ई (A-I-e-e-yA-I) rule

Examples
He should eat mango -> त्याने आंबा खावा (tyAne AMbA khAvA)
He should eat tamarind -> त्याने चिंच खावी (tyAne chiMch khAvI)
She should write the letter -> तीने पत्र लिहावे (tIne patr lihAve)

1) When the subject is You(singular) i.e. तू(tU) ; extra स(s) is appended to verb form.
You should eat mango -> तू आंबा खावास (tU AMbA khAvAs)
You should eat tamarind -> तू चिंच खावीस (tU chiMch khAvIs)

2) Sometimes extra त (t) is added to plural form. So both are acceptable forms.
He should give all answers-> त्याने सर्व उत्तरे द्यावी / द्यावीत (tyAne sarv uttare dyAvI/dyAvIt)

3) For अकर्मक(akarmak) verbs i.e.verbs that do not need noun; you can create such statements by using neuter-singular form.
e.g.
He should go -> त्याने जावे (tyAne jAve)
We should laugh -> आम्ही हसावे (AmhI hasAve)

4) Some verbs which end with other sounds like ए (e) ऊ(U) ई(I) etc. ; forms are little different. Such verbs are very less. So more you read Marathi you will understand it better.
e.g.
To drink -> पीणे (pINe)
पी (pI) + आवा (AvA) -> प्यावा(pyAvA)
प्यावा-प्यावी-प्यावे-प्यावे-प्याव्या-प्यावी (pyAvA-pyAvI-pyAve-pyAve-pyAvyA-pyAvI)

To wash -> धूणे (dhUNe)
धू(dhU) +आवा (AvA) -> धुवावा(dhuvAvA)
धुवावा-धुवावी-धुवावे-धुवावे-धुवाव्या-धुवावी (dhuvAvA-dhuvAvI-dhuvAve-dhuvAve-dhuvAvyA-dhuvAvI)

To come -> येणे (yeNe)
ये(ye) + +आवा (AvA) -> यावा (yAvA)
यावा-यावी-यावे-यावे-याव्या-यावी (yAvA-yAvI-yAve-yAve-yAvyA-yAvI)

Try creating sentences with different verbs using above rules. Crosscheck them by creating same by “verb forms” feature on https://learnmarathiwithkaushik.com/