Build racket head and body fakes into your return of serve. Essentially try to make the opponents think you are going to hit in one direction, then hit somewhere else. You can do a simple racket head fake by showing and holding the racket face up in front of you, as if you are going to do a net shot, and then flick, slice, or dab at the bird at the last second. Both types of racket head fakes force the opponents to stop anticipating and wait for your shot. It is much less tiring and mentally easier to play against people who are predictable in terms of shot selection and shot execution.
Next time drop the serve to the net.
Next time fake straight and drive cross court to the back. The point here is to be attuned to the adjustments the serving team makes to return your return. Vary your returns anyway, since all returns become more effective if the serving team cannot anticipate what is coming. This is not so. You want to jump quickly forward, but also you want to control your momentum since you might be able to put the next shot away.