I've read that the gastroc is most commonly injured, but don't recall the exact citation. Standing calf raises, according to "Complete Conditioning for Tennis," will target both the gastroc and the soleus. If you want to target just the soleus, you can sit down and lay a barbell on your thighs and lift from your toes. Both these exercises are, in a way, also neuromuscular conditioning. If you think about it, in tennis you're pushing off your toes quite a bit from a standing position, sometimes from a partial squat. When I went through PT, they also had me train glutes, hamstrings and quads, doing stuff like the leg press. It took the load off the calves. And yes, proper dynamic warmup is key--putting your body through the range of motion you can expect in a tennis match.