whenever he tries to walk forward, wherever you are in the stage of getting on, calmy sit in the saddle, halt him and make him back up to where you were originally. Don't make a fuss, just do it. When he stands there for a couple seconds, give him a small pat, walk forward a couple steps, then dismount. Then repeat this session til he realizes how much easier it is to stand still.
For hte butt swinging out problem, have a friend help you. Have him/her stand near his rear (haha that rhymes) and if he tries to side step, have your friend tap him and get him to stand in front of hte mounting block.
One more way that I geuss is kind of for both to get him to stand still would stand on top of hte mounting block, and have him walk cirlces around it, and if he tries to stop keep him going. Then, have him stop infront of the mounting block. If he tries to walk anywhere, send him off again until he stands completley stil and reward him with a lot of pats! This is a little like joining up in hte sense the point is to get them to WANT to stand still so they do not have to walk again.