http://boards.cannabis.com/grow-faqs...made-easy.html is a good FAQ about how to fim and top; it even has good pictures to assist in the details of where and how to fim and top.

As for fim'ing and/or topping during flower, I was advised not to do that either. As locomark stated above, it will take much needed energy away from bud production and therefore could be counterproductive. You could try lst'ing your plant, by tying it down sideways to allow lower bud areas to have more direct sunlight, thereby ensuring better overall bud development. There are plenty of threads on this board about lst'ing, just do a search for it if you have any questions or need further details.

Be good out there!