Here's a great idea to help you meditate. This is one of the most effective ways to draw your focus to the present moment and it's extremely useful on those days when your mind keep racing away.
You simply count when you breath in, and pause as you breath out.
This gives you something to focus on and helps to stop your mind wandering. Just count up to ten, and then start again.
You can try this when you're out walking as well to really bring your mind into the moment. You may have tried this before as well, as it's exactly the same as counting sheep when you're trying to get to sleep.