... start playing lots of doubles with good doubles players...
If your fellow players are of a high standard - for doubles, rather than just singles - you'll be forced to play S&V on all your service games, on both first and second serves. So, that'll give your volleying plenty of practice. But also, the good thing is that you'll only have half the court to cover, so - provided you have played a half-decent serve - in most instances you'll be able to get your racket to most balls that come your way, rather than being passed outright. Hence, you'll get a chance to intercept blistering returns that if you were playing singles - because of the extra width available to your opponent - you wouldn't get a sniff at. So, good practice in a match situation.
The second thing you learn when you play doubles is to place your first serve - you take a fraction off the pace, but you nail the spot you want to nail. If you like, you learn to crank up your second serve closer to the pace of a first serve, but you still retain some of the extra safety features of a second serve, such as spin and/or placement. For instance, a very effective serve for singles S&V is the slider from the deuce court (or for that matter, the kicker from the ad court), that takes the returner wide and opens the court for a cross-court volley. In either case, if you're playing such a serve as a first serve you will never hit it flat and hard, you'll play a hard kicker (i.e. a hard second serve kicker, trying for extra kick) from the ad side. From the deuce court, you'll play a sliced serve (or topspin serve, or a mixture of both) that goes over the lowest part of the net - here, what you want from the spin is to keep taking the ball away to the side, and the reason for adding top (rather than pure slice) is that it enables you to aim for a very acute angle higher up the sideline, with the topspin bringing the ball down and in and then making the ball kick to the sidefence. In either case, slightly slower but well placed first serves - when playing singles, will give you extra time to come up for volleying.
Two things you need to watch when playing wide serves where your partner intercepts the return are the quality of the return and the position your partner intercepts them, because that's the position you'll have to get to when playing singles to intercept them. Put it another way, if on your wide serves from the deuce side your partner usually gets a hard down-the-line pass which he just manages to volley with his backhand (assuming a righty), then if you play the same serve in singles you'll get passed/killed because you won't be able to cover it - basically, your serve is not wide enough and falls nicely into the returner's strike zone (and you'll also see a fair share of returns coming back to you, either down to your shoelaces or hard and wide to your forehand, again a sign that you're serving plum into the returner's zone). On the other hand, if he gets weak floating returns which he puts away easily, then your wide serve is working nicely for singles S&V also.
AG100s:- MSV Hex 1.10 54/50