My Fender Stratocaster doesn't hold a tune very well...what can I do?

I have a Fender American Deluxe Strat and it just doesn't stay in tune that well. Originally the bridge was floating, but I've since fixed that so it's more or less flush with the body now. But the tuning is still finicky. Any tricks or tips to help it keep in tune better, or is that just the way the guitar is? Thanks