With modal verbs (could, would, may, might, must,...)

Ex:He should have studied harder

After verbs such as: appear, claim, expect, hope, happen, promise, seem,...

Ex: He appears to have drop out of school

After certain verbs (say, believe, think, consider, suppose, understand) in the passive voice

Ex: Sofia is believed to have magic powers

To express purpose

Ex: She went to market to buy some bread

After: would like, would love, would prefer

Ex: I would like to go to school by car

After: the first/ second/ next/ last/ best, etc. instead of a relative clause

Ex: She was the last to hear about my family

After certain nouns (pleasure, shock, etc.)

Ex: It was a shock

After some, any, no and their compounds

Ex: She doesn't have any books to read

After the following structures

Ex: It is very suitable for you to apply for this job

With too/ enough:

Ex: I do not have enough money to buy this smart car

After only, for emphasis or expressing disappointment

Ex: I bought that hat only to take a picture

At the beginning of the sentence, as a subject or in fixed expression

Ex:To get up early, I never stay up late.

After verbs followed by a question word (who, what, which, where, how, but not why): ask, decide, remember, understand, decide, tell...

Ex: Can you tell me how to make that cake?

After certain adjectives: afraid, amazed, anxious, astonished, careful, determined, glad, happy, surprised, upset, willing,....

Ex: I really glad to meet you

After certain verbs (as their object): afford, agree, ask, beg, claim, decide, demand, deserve, expect, fail, tend, threaten, volunteer, want,.

Ex: Do you remember to turn off the light?

After the object of certain verbs: advise, allow, ask, beg, cause, challenge, invite, need, order, permit, persuade, remind, require, teach, tell, urge, want, warn..

Ex: My mother allow me to go to school with my boyfriend.

After most modal verbs (can/ could, may/ might, will/ would, shall/ should,...)

Ex: You should wake up early in the morning.

After: would rather, would sooner, had better

Ex: I would rather go to school by car

After the verbs hear, let, listen to, make, notice, observe, see, watch, etc. These verbs (except for let) take the full infinitive in the passive voice.

Ex: I hear he sing a song

Ex: Why not have another hat?