Learning to make a sig from no experience can be hard. Most people will start by making sigs at clan websites and other gaming related sites. A lot of the time the other designers at these sites have very little experience. This means that trying to learn there is virtually impossible. Always surround yourself with people who are better than you, and you will improve. I suggest start learning without even opening up photoshop. Get to know what makes the difference between a good sig and a bad sig.  Read tutorials and talk to other designers.  Don’t waste time making sigs with downloaded brushes and a out of color halo render.  Always shoot for professional right out of the gate.  If you understand the basics of sigs you will become a better designer ten times as fast.