Aimlabs

I'd say the easiest task to do is the grid shot 3x3 task. It is only 30 secs (and will immensely help with the complete 'x' amount of tasks achievements as well.) This is very easy to do just start up a game with then hit the balls at least 1 time then on the next try get a higher score then your previous score, with loading times this should take less than a minute and ten to twenty seconds to do.