^^^ I just start with 83% of my inseam measured from floor to chamois. Use a book with a 1-inch or so binding. Stand with your back and heels against a wall. Then pull up the book with some force into your crotch (to simulate you sitting). Keep the edge of the book against the wall. Then have a friend mark the wall at the top of the book with a pencil. You can use the online guides like the one linked to above to play with saddle fore/aft, cleat position and stem length. Ideally, I would go to a a good bike fitter that was recommended by other riders and/or shops. He/she may charge you a lot to do a complete fitting. But its money well spent since it should do all of the above and also take your flexability into account to help with stem length, handlebar height, etc.