Know when to follow a verb with the -ing form or with to + verb.
The -ing form acting like a noun — swimming is fun.
To + verb — purpose, ability, and the verbs that call for it.
Which verbs take a gerund, which take an infinitive, and which take either.
Verb + person + infinitive — I want you to stay.
The infinitive without to — after modals, and after let/make/help.
Same verb, different meaning — remember to call vs. remember calling.