I've been kinda wanting to get back into doing demo reviews lately, but that's something that won't happen for a little while.
However, the most obvious things I can say about any medic that is below invite level is that their positioning and game-sense are their biggest problems. Minimizing damage thrown in your direction and playing your angles properly are imperative. On top of that, knowing when and where to expect bombing soldiers, sticky traps, possible flanks, and using all sound to your advantage will also make you expontentially better. You can be mediocre at just about everything else and still be better than most.