Verb+ing

Use verb+ing
- some verbs (enjoy, finish, go on, hate, like, love, (don't) mind, spend (time), start, stop, ...) (parecen verbos referentes a sentimientos o pensamientos, ver comparación con to+Infinitive)
- as the subject of a sentence: Smoking is bad for you.
- after prepositions: He left without saying goodbye.

(remember the Spelling rules for the -ing forms)