Be sure to have prior knowledge of card forces, card manipulations and similar fundamentals. If you do not know how to do anything, what is there to misdirect?
Do not abuse misdirection. The key to misdirection is subtlety, and it can become subconsciously annoying to spectators if heavily repeated.
Be natural. The whole key to misdirection is that the spectator trusts you. If they smell dishonesty, then misdirection will be lost.
Direct your eyes, conversation and body language to the opposite side of wherever you need the spectator to NOT look. If you are manipulating a card in your right pocket, avert everything to the left side.
Keep all focus on the spectator! Magicians get so arrogant that they sometimes forget that the humbler you are, the more of a trust that will be built.
Getting a spectator to talk about herself will do two things: it will keep her from watching you and it will get her to think you are a friend and therefore trust you more.