1) After prepositions like: about, without, to, for, from, on, of
2) After specific verbs like: hate, stop, prefer, enjoy, avoid, remember, refuse, to mind, keep, spend
3) As subject of a sentence
4) After some words/expressions: feel like, it's no use, it's worth, there's no, be busy, can't help
After verbs: to stop, to remember, to forget: gerund OR infinitive