For Me....
1. Staff. Get the best staff available. Its vital that your players at that level get the best training possible
2. Sign any decent players (5* or better) on Full Time contracts. It will cost you a bit more, but they will train full time, and improve better.
3. As has been said, scout the hell out of where ever you can. It's important to find players all year round, as you never know when you'll need one.!
4. Tactics. At this level, tactics are everything. Visit the Tactics forum, or teach yourself, but spend time developing a successful tactic.