Play with a weak opponent.
Tips on how to get more forks?
Go to the local store, and buy some forks. I'm curious, so do you eat with spoons or with your hands?
Welcome to 2015.
I am very close to your level. Or we are close to each other. Which ever the case is our problem, I think, is we are trying too hard to follow principles and exact opening lines and theory instead of just playing. I find just playing as if your new(so to speak) leads to both rookies being confused, thus leading to forks.
Or you can spend hours upon hours studying openings, only knowing openings, find out which opening can produce forks and then, I guess, start middlegames or something.
Yuri Averbakh, Chess Tactics for Advanced Players argues that the double attack is at the heart of chess tactics. A fork is a particular form of double attack in which one piece attacks two that are not on a line. If they were on a line, it would be a pin, skewer, or X-ray. A knight can fork, but cannot pin. This limitation is also true of pawns and kings. The other three pieces are capable of attacks along a line as well as forks.
Aside from this quibble over the correct terminology, I refer you to Ziggy's excellent discussion of Reti's study.