Gerunds and Infinitives: Preposition + Gerund

One of the most reliable rules in English is that prepositions are always followed by gerunds, never infinitives. After about, at, by, for, from, in, of, on, to, with, and all other prepositions, use the -ing form. "I'm interested in learning" (not "interested in to learn"). "She's good at cooking" (not "good at to cook"). "Thank you for helping" (not "for to help").

This rule applies to all adjective + preposition combinations: "tired of waiting," "afraid of flying," "excited about travelling," "sorry for disturbing." It also applies to verb + preposition phrases: "think about going," "succeed in passing," "prevent me from leaving," "rely on having." The only confusing case is "to" — it can be a preposition ("look forward to seeing") or part of an infinitive ("want to see"). Test it: if you can replace the verb with a noun ("look forward to the meeting"), then "to" is a preposition and needs a gerund.