What has recently improved my game is developing my pieces. You don't have to play aggressive at all. You just move out the correct pawns, bring out your knights to guard the former, pull the bishops out to eye down long diagonals but still near your king, then, castle. What you'll end up with is plenty of protection while threatening large developments from your opponent.

Learning a few solid openings, (Ruy Lopez is my favorite for the amount of options it gives you) will help you learn how to do this. Just worry about getting your pieces mobile before you plan your attack.

When you get that down you can start exploiting weakness and preventing attacks before they have a chance to develop.

On youtube this guy Kevin under the handle "thechesswebsite" has some pretty solid videos where he talks about different openings and what the strategies are. Hope this helps.