First understand what meditation is not. It is not merely sitting in a room thinking. Sitting quietly in a room can be a wonderfully relaxing exercise but it is not meditation.
First find a quiet, cool space. Sit comfortably with your back straight. You do not need to worry about a certain formal position at this point. Again, back straight, breathe deeply, slowly and regularly through your nose. Hold briefly and then exhale slowly. Do this rhythmically. Focus on your breathing. Some people like to use a candle flame or other source of focus.
Now, comes the tricky part. Focus, without effort, without frustration on your breathing. When your thoughts wander gently move them back to center. You mind will rebel and try to think about every thing under the sun. Don’t be frustrated this is normal. Just gently move them back as many times as necessary. Do this for as long as it is comfortable. Ten or twenty minutes is generally sufficient. You are not goal oriented here. What happens happens and that is fine. Mindfulness is like pinning quicksilver under your thumb. The harder you “try” the harder it becomes. This is a natural organic process let it happen without striving. For the first two years of your life you lived in mindfulness. You are returning to a natural state. It gets easier and more pleasant as you practice.