Actually, these shots show some promise, to me. For being your first time trying this, you seem to have pretty good timing. Compositionally I find them interesting as well. I would maybe change a few, like #1) I would pick which third you would like your subject in. The right hand placement is good, but I'm not a fan of him in the center third. That's just me. It is also perhaps the weakest in terms of timing.
#2) Great timing. The tennis ball is even deformed. The composition works as well. Only complaints of the basics are the pole right behind the racket and the relative lack of separation between the fore- and backgrounds. The two are related in a way, because with a shallower d.o.f., the pole would be less visible.
#3) This is, to me, a little uninteresting. I don't fully get a sense of action in the shot. Compositionally it's fine but overall, not that great.
#4) Great shot. A little late on the timing, perhaps, but not by much, but the subject is frozen and has an expression that shows he's really trying. The comp is a little funky. I like it, because you usually see action shots like this cropped tight on the subject and vertical, but this is different, which makes it more interesting. Conversely, it is more standard procedure to crop in tight and you might really get a sense of action then. Keep a little ground beneath his feet in there for context, and the ball as well if possible, but turn the frame vertical and there you go. I'd say try it. Whether or not you like it is up to you.
#5 & #6) These are pretty much in the same boat for me. They are good shots, framed well technically. They have a decent sense of action in them.
For the set as a whole: Shallower d.o.f. and maybe try to crop them tighter on the subject. This is more typical of sports shots as the athlete is typically the main focus of the event and you usually want to reflect that in your shot. Again though, these work for me. It just depends on where you want to take it.
Now for looking soft, I would agree, they are a hair soft, but doing some minor post process sharpening could really help these. Don't go overboard. Subtle is better. Also, bump up the contrast. I would say quite a bit, but it depends, since I love high contrast stuff. Still, higher contrast will make them pop more. The lighting plays a factor here since it looks overcast and that tends to really flatten out a scene.
Overall, nice job. Keep practicing, it'll come with time.