Instructions
Examine a solved cube and note there are three distinct types of pieces. These are centers, corners and edges. For centers, white is always opposite yellow, orange is opposite red, and green is opposite blue.
Mix up the cube with only three or four turns, and resolve the cube, carefully noting the positions that require moving. Continue mixing up the cube slightly more every time, eventually ending up with a totally random cube.
Solve one face to begin. Assuming you have solved the cube before, you should now recognize that you haven't solved the face until the colors that touch the edges are correct as well. Remember, the edge and corner pieces are not independent of the other sides of the cube. Starting with white, create a cross/plus sign on top of the cube, and then position the corners until you have solved the entire layer.
Flip the cube upside down so the white face is now on bottom, and solve the middle layer next. You should be comfortable with the way each piece of the cube can move and how to move them without disrupting the solved faces you have already created.
Solve the top layer next. If you used white on the bottom, this will be the yellow face. Begin again with a cross, and then position the corners. If you have solved this correctly, it should be one or two turns away from totally finished. Align the correct edge to the correct face and it's done.
Mix the cube up, and begin again. Commit these steps to memory, and learn to solve the cube by process, instead of by color. With practice, it will become more fluid and quicker. You will learn how to solve every problem you encounter in the minimum number of moves.
Time yourself. Compete against yourself or others to see who can solve the cube the fastest. Solve with one hand, with your feet or blindfolded. If you think you've mastered the cube, find a new way to solve it or a new group to compete with.