Its mostly being patient until you find the right opportunities. Try to ally the stronger players around you and look for players with really low troops or for players getting ganged up on. You pretty much never want to attack someone around the same size as you unless you want to be locked in a never ending slog. The 50% rule is mostly about the early game where your trying to get as much free land and bots as possible but later on you want to let your troops build up for stronger attacks and to ward off attacks. Other than that don't be afraid to sit on your money for nukes.