Well, because of the general incompotance of referees regarding scrums, there is little things you can do to cheat your way out of a losing scrum. As a tighthead, there are two very easy things I tend to do, if their pack is generally bigger and stronger than ours. First, on your hit, you want to get as low as you can, and look for his arm going on the bind. From there, pull his arm down to the ground and rotate your neck. It'll mean the scrum collapses, but generally they'll eventually get pinged for not getting their bind up. If that's not working, just straight-up grab the looseheads outside arm, and pull it inwards, meaning that his body will have rotated inwards and he won't have a straight platform to push. Most referees won't notice, even when standing on your side of the scrum.
If you are winning, then you shouldn't change too much. Just make sure that you get lower than the opposing prop, and try to get underneath him on an angle, and push. The aim is to make him stand up without losing your positioning.