Every turn you have a goal in mind; clear the enemy creatures. When looking at your hand and deciding which cards to use to do that, you should first try to do it using the fewest number of cards possible, and then if that is equal, try to do it using the "worst" cards possible. By that I mean, the cheapest casting cost/most flimsy/least effective creatures.
To use an obvious example, if you're trying to kill the enemy's Argent Command who has lost his bubble, and in your hand you have a Bluegill Warrior and an Argent commander of your own, it's probably best to use the Bluegill Warrior and save your own Argent Commander for a better use. (An exception to this being, using the Bluegill wil