If your going to mug the guy remember your not always going to survive the move. Sure it's a bonus if you do but don't get too hung up if you don't.
The best way to do it is to run up, put two balls in his face and get back around his bunker. Running straight past is a risky move because if you miss him your screwed, plus his team mates will already be mowing you. As for the best time, you should be looking for several things, pots flying up in the air, paint coming out of the other side of his bunker. My personal favourite is wait to hear him make a call, if he's shouting to his team his attention is about 80% on making the call and getting a reply, and only about 20% on you.
Muggings are good fun, but it's a fine line between doing it properly and making a twat out of yourself. Oh and making a twat out of yourself hurts alot, try not to do it.
Good luck,