This is going to sound a bit nuts - but I think that in some situations, it can be an effective technique. If you act stupid or like a bludger, it may cause some people to discount you as a threat. Although that doesnt seem like a big deal, it can cause some people to develop a false sense of security. I remember when I was in year 12, with economics the top 2 or 3 guys acted like the biggest bludgers in class, but come exam time they pulled out massive marks. For some reason, their whole bludger routine somehow spread throughout the class (I think most people saw that they were bludging and this made them feel less guilty about their own procrastination). Even after these guys kept getting big marks, most of the class kept thinking they were bludgers (you would be suprised how slow people at to catch on). I know this whole response sounds ridiculous, but the OP shouldnt be laughed off entirely - it think its a case of "so crazy it might just work". But seriously though, the best strategy is hard work.