I have several of the bad habits already mentioned here, so I'll just list two more:
(1) Spending too much money in the first two or three recruiting cycles instead of being patient to watch how things develop (although I am improving in this area, finally, after getting burned SO MANY times).
(2) Getting enamored with recruiting a big man because of his ATH, DEF, and LP, then realizing after signings that the highest REB rating on my team is 66.