There are many, many wonderful stories about the Ba`al Shem Tov. Here's a teaching that is simple and direct but has great appeal to me right now. I love this first sentence:
When you want to pray, it should be with awe. This is the gate through which one enters before God. Say to yourself, “To whom do I wish to bind myself? To the One who created all worlds with His word, who gives them existence and sustains them.” Think about God's loftiness and greatness, and you will then be able to enter the supernal worlds.