LEARNING THE COMBOS!

[raadamiir]

This one's pretty basic. Knowing which Keepers go together and which ones don't is vital when that Keeper Limit card gets played.
For example, a common mistake is thinking that War and Peace go together, and retaining them both, when it would usually be better to toss the War card in hopes of winning with Peace, no War. Of course, if that goal recently hit the discard pile, you might want to discard them both in order to keep more promising Keepers, which brings me to my point.