The way I decide what cards to use is a method I call the MOCS (Multiplication of Card Stats) system. To use the method, I multiply the attack of a card by the health and get a number. The card with the highest number (out of the cards that are possible to choose) is the card I use. Cards like Irradiation and Asylum I use when they show up. Also, when there are two numbers that are the same (e.g. two cards that have a total product of nine), I look at the green text (It shows up under the current health when you roll over a card) on both cards and rule one out. --- If you think this method works for you, plus it up and then use it.
I was intercepting an Oozle, and a Biter came up and tried to kill me. The Oozle looked at the Biter like it was saying, "I'll handle this", and the Biter left. The Oozle then killed me...