Most players know what a third-ball attack is: you serve, the opponent returns, and you attack aggressively, usually with a loop, a smash, a hard-hit drive, or perhaps a quick off-the-bounce drive. It's that simple. But this means you are relying on your opponent to return your serve in a way that you can attack effectively. While you want to develop your third-ball attack, you also want to develop your five-ball attack as your fallback plan.
What is a five-ball attack? You've probably already figured it out: you serve, opponent returns, you attack in a way to set up your next shot, opponent returns, and you attack aggressively (often with a smash or loop kill).
A five-ball attack often is just a third-ball attack with one more shot. But if your opponent is making your third-ball attack difficult, you might want to vary it with a shot that's more difficult for your opponent to keep you from doing.
In the "classic" five-ball attack, you serve backspin, opponent pushes back deep, you slow- or medium-speed loop, opponent blocks, and you end the point with a smash or loop kill.
A deep, spinny loop is difficult to return without setting up your next shot. Depth is often most important - a slow loop that lands short on the opponent's side is easy to attack. (The exception to this is against a counterlooper who's too far off the table to react quickly to a slow loop that lands short.) A deep loop is much harder to return effectively. Plus, the very slowness of your slow loop gives you time to get into position for the next shot. This is why you can slow loop from the backhand corner with your forehand, and still be in position for the next shot, even if you aren't very fast.
Placement is key. The best place is often right at the opponent's middle, the transition point between forehand and backhand, usually right at the elbow. This forces them to make a quick decision between forehand and backhand, and often leads to a weak or inconsistent return. Or go wide to the corners if the opponent has trouble covering them. A deep, spinny loop to the very wide backhand can often cause havoc.
Many players have trouble serving and looping if their opponent pushes the serve back very heavy. This may mess up your third-ball attack, but it plays right into your fifth-ball attack. Use their backspin against them; let the ball drop slightly more than usual, and then really topspin away with a slow loop. In fact, sometimes don't even look for a third-ball "attack"; decide in advance that, unless you get an easy ball, you will serve and slow loop. This will help make your slow loop even more consistent, since there's no indecision.
Finally, remember that you don't have to force a put-away with the fifth ball. If the shot isn't there, don't go for it; just play another aggressive shot if possible, and focus on the next ball, and so on.