First of all you have to need a bonsai and scissors. In the type of the tree shown in the tutorial which is a fifteen year old, once you have got the branch structure established then you can prune the leaves over it. Start from the bottom branch chop of the leaves that are out of symmetry with your scissors. Cut from the outside to the inside. Now move towards the upper branches. Chop off extra new branches which are coming out from the main branches. Reduce the leaves in a fine length all along the branch. Cut in such a way that the leaves are cut off from the bottom of the branch and allow the leaves from the top to continue. In the middle if there is any weak branch then shape it properly. When you have reached the top of the tree, then check the tree all over and finish any left over leaves. That's it.