There are many different ways to meditate but this is the way I do it.
I started with a Mindfulness Meditation where you focus on the breath. Now, when you focus on the breath, you focus on the sensations of your breath while "letting go" of any other thoughts that pop into your head. I bold the word sensations just to emphasize the fact that you are trying to do nothing but experience the sensations of your breath. You may notice the sensations of your breath strongest either at the tip of your nostrils or around your chest. If you catch yourself drifting off in thought, just calmly return your concentration to experiencing the sensations of your breath.
Sounds easy but give it a try! Thoughts will pop in your head against your will. The things you realize during meditation will have a great impact on how you conduct yourself.
Here is a good guided meditation by Sharon: