This is not the “soft serve” you get in the frozen yogurt shop, but INTENTIONALLY serving softer to win the point. When should you do this?
Any good player will get used to seeing the same shot over and over. So even if you have a good serve, if you hit it the same pace in the same place most of the time, your opponent will get the timing down and take away your serving advantage.
In addition to varying the location of your serve (which is the first thing you should be doing), you should also change the pace of your first serve. After serving a solid first serve one time, try coming back with a slightly slower serve to the same location on the court.
Odds are, your opponent will be a little out in front of the ball and may not take the extra step in that they should – which will throw off their return of serve.
Also in doubles, the slower serve will give you more time to get to the net and make a better volley. Like the professional pitcher, try “pulling the string” on the shot to maintain the serving advantage.