Preposition + - ing

If a preposition:
- in
- for
- about
- at
- on
- with
- of
- for
- instead of
- in spite of
etc.
is followed by a verb, the verb ends in -ing.

I'm not very good at learning languages.
Are you looking forward to seeing Ann again?

before -ing and after -ing

Before going out, I phoned Sarah.
What did you do after leaving school?

(Before I went out ... and ... after you left school)

by - ing
She made herself ill by not eatng propely.

without -ing
I ran ten kilometres without stopping