This achievement counts both goals and assists, but unfortunately it only counts them in real Online matches and not private ones. That being said, this should come naturally as you play the game. Since it counts assists as well, you don't need to be that skilled to unlock it.
A goal is obviously when you make it into the opponents goal (your own don't count!), and an assist is when you touch the ball in some way right before a teammate makes a goal. There's no real way to boost this and no trick to doing it; just keep playing matches and trying to score. It's that simple.
Side note: It does not retroactively count goals and assists, meaning you have to get 30 as of this update to unlock the achievement. Your previous stats are not counted at all.