Make sure that you memorise any facts and formulae that you need to know.
Learn properties of shapes and angles by drawing diagrams and colouring.
Draw spider diagrams (or mind maps) to link together what you know about a topic.
Most of all, do plenty of practice.
Use websites such as www.mymaths.co.uk and www.waldomaths.com in addition to written exercises and worksheets, but whatever you do, don't expect it all to just be in your head!
As Aristotle said, "That which we must learn to do, we learn by doing"