Fail to prepare, prepare to fail ~ or something like that! Harsh but fair in most cases but proper preparation isn't that hard and to what extent you prepare is down to original condition and materials, what finished look you are going for and what its end use will be. One rule, no matter whether you're a stripper, sander or scuffer, ALWAYS be a scrubber first! Cleaning is one of your most important steps, and don't be fooled by the clean, well looked after pieces. They're the worst! Years of being lovingly waxed or polished has created an adhesion barrier. You need to roll up your sleeves and put in the graft before you get to the pretty bit!