Go after a max free agent who you expect to be a multiple-time all-star over the next five years (or try to trade for one). If you think a player is unlikely to do that, don't bother if his salary level is anywhere near the maximum.
If none is available, only sign players to one- or two-year contracts, even if you have to overpay a bit (such as Kwame Brown's contract), while trying to acquire trade assets. Repeat every off-season until you acquire a legitimate championship core.