This video shows you how you can self treat those tight spots in your muscles, also known as trigger points.
All you need is a little ball (hockey/tennis/squash), and to use it to apply pressure to those trigger points. The firmer the ball, the deeper it will work into the tissue. I advise to roll around until you find those nasty knots which will be tender and may radiate to other parts of your body. Once you find the tight spots, stop rolling and hold until the tightness/pain eases off. This will usually last between 20 - 30 seconds. Easy.
Trigger points will normally try their best to return so it will usually take many goes on the same knot over several days to weeks. The more you work on them, the less bothersome they become.