From an excellent sermon by John Piper:
Pray everywhere. Keep the green button on. Let the most natural breathing of your heart be Help, Lord! and Thank you, Lord! When Peter began to sink on the water, he cried, “Lord, save me” (Matthew 14:30). The father of an epileptic boy cried out, “I believe; help my unbelief!” (Mark 9:24). Anywhere, any time, cry out to him. Live in his presence so that this is not an awkward moment. Speak to him often so that your conscience does not condemn you as a fox-hole Christian—only talking to God now and then to save your skin. He loves to save your skin, but he loves even more be your friend.
You really need to read the whole thing here. Or even better, toss the MP3 on your iPod and listen in the car.