As you sit, and focus on your breath, other thoughts will come into your mind. You will likely start to get bombarded with random thoughts like: the shopping list, sending that email to a client, worrying about something you said or did. Thoughts will race. This is normal. As these thoughts occur, just gently brush them aside, remember to relax the body, and go back to focusing on the breath. As you continue your practice you will get better at this process.
How long someone should meditate is totally up to them. I think that if you are just starting out, you should try for a length of time that you know you can do and go from there. Use a timer once you start. Can you start with 5 minutes? If so, start there and add more time as you go. However, as with anything you are trying to do and become proficient, it is the frequency and not the length of time that is important. If you meditate for five minutes every day, you will start to feel benefits. If you do half an hour once and then maybe ten minutes a week later, it won’t have the same effect.
Now that you have some tools to work with, try it out for yourself. In the near future, I will do a second part to this piece and provide some other techniques, such as visualization, that can be included in your meditation practice. For now, just find a quiet spot, set a timer, and get internal. What are you waiting for?