1. At 6'1, 180 and lefty get that serve working. If you can hit the lefty swinging slice and the T serve at will it will earn you oodles of free points. 3.5's and low 4.0 lefties tend to rely on the swinging serve to the righty BH so much so that folks can sit on it.
2. Get to a point on either your FH or BH where you have no fear unleashing on mid court balls.
3. When playing most 3.5's and junkballing 4.0's footwork, footwork, footwook, and don't get impatient.
4. As for return of serve just worry about getting the point started in a way where you are not at a severe disadvantage. Giving away free points in singles off the return of serve is just bad.