When serving, don't look for a ball to attack. Unless the receiver does something to stop you from attacking, serve and attack over and over. If you aren't confident in your attack, then this will make your attack much stronger and turn you into a better player.
There are tactical exceptions to this, but they are relatively few. Defensive players such as choppers and blockers might serve and only attack if they see a relatively easy attack, but even they should look to serve and attack every chance so as to develop their attacks. Against a receiver with a weak attack you might tactically wait for a better shot rather than force the attack off your serve against a relatively good return - but even there it's good practice to serve and attack so you keep getting better at it. Sometimes it's good tactics to catch your opponent off guard by not attacking, such as a sudden drop shot or quick push against a player expecting you to attack and not ready to attack themselves. But generally, and perhaps even relentlessly, you'll find more success if you serve and attack whenever the receiver doesn't do something to stop you from attacking.
None of this means you have to serve and rip a winner every time. You only do that if you do get a relatively weak return. Attacks should be varied - forehand or backhand; hard, medium, or soft; usually deep, but when attacking more softly vary the depth; to the opponent's middle (elbow) or wide corners, or even outside the corners; and with varying amounts of topspin and sometimes sidespin. Never serve and blindly attack; attack, but attack with purpose!