It helps to rub everything with a bit of alchohol, need to make sure its all clean. Plug the muzzle with some expanding foam and tape over that. For optics, put alot of cotton balls in and tape that as well (don't leave the cover on it, paint seperately). Don't paint over any screws, parts that rub together, or any cracks, make sure those are all protected. Start with the lightest color first and end with the darkest.