The biggest variation I see amongst us common folk is the misconception of where the 28-foot mark really is. This is important, because as a T, you are supposed to set up at this depth. How many times do you see the T being within a couple steps of half-court when the ball is below the top of the key? Two things to remember. First, you should never let the ball get behind you as the T in the half-court--it's OK to be at half court when the ball is out front, but as the ball moves north-south towards the basket, and eventually goes below the top of the key, you need to slide down with it. Second, the 28-foot mark is no more than 1-2 steps higher than the top of the key. Think about it, top of the key to the basket is 20, and there is probably 5 feet between the basket and endline. Dial that in!
C's also have a tendency to work very high. I see a lot of C's working in the T position, at the 28- foot mark. You need to start at the foul line, and perhaps work a step or two in either direction, when you need to get an angle. You should never be any higher than the top of the key, and never lower than a step below the foul line.
As the C, when the ball swings to your side, you may have to come up higher to get the angle on your match-up. And that's OK! Why? Because if you have a match-up in your primary as C, over 90% of the time the L should be rotating over. If you go higher, or "top-side" to take the ball match-up, you will wind up at the depth to be the new T anyway. However, remember that if the L does not rotate, and the ball match-up goes away, return to the foul line base position, otherwise you have created 2 T's, which is a no-no.
L is an interesting place. Guys on TV seem to work almost exclusively in Window 1 (edge of key) and Window 2 (halfway between edge of key and 3-point line). You also should be a step or two off the line. The T is there to support you on travels in the post, so you can be closer to the floor. The rule of thumb is, you should be able to see the front of the rim as the L.
Last positioning issue--taking your on-ball match-up. When the ball is in your primary, that is your focus. You have the ball and the defender. The other 2 guys can take the other 8 players. Aggressively take that match-up. Move closer to the match-up, move to keep the angle you need to see the play, and square your body to it so your partners know you have it. Lots of people take the match-up, but don't move a lot physically. Send the message to the partners and everyone else in the gym that when the match-up in your primary starts that you own it, and your focus and attention is nowhere else. It will help you do better, help your crew focus more on the off-ball players like they should be anyway, and the perception of what is going on with the crew.
So how does this help?
1. It will give you better angles on plays, especially if you move and stay physically active on match-ups in your primary.
2. It will reduce the number of long-distance calls you make, which helps with perceptions. Even when you're close, you don't want to be doing that very often.
3. It will force you to stay engaged on rebounds, not "cheat" back on shots. This is a very common "ding" when evaluators observe and rate/comment.