At the start of the game, call out "mid or feed". This will show your teammates who is boss, and establish yourself as the alpha pack leader of the team. Pick a carry hero and head mid, making sure your allies buy the courier and wards. While mid, focus on getting as much farm as possible. If you have trouble getting farm, abandon the mid lane and head to the jungle. At no point should you bother helping allies in the other lanes, they will feed regardless of you going to their lane. Don't bother defending any towers except the ones in your base. If at some point you find yourself in a team fight, stay in the back until after your allies have fed, and then pick off any low hitpoint heroes if you can. Turtle in your base until you have enough farm to solo the entire enemy team with some big plays. This strategy has a 95% success rate in the top of the very high bracket.

Summary:

• Mid or feed
  
• Never buy courier/wards - it is unacceptable for the hero mid to buy these items
  
• Don't bother helping allies in other lanes, they will feed even if you go there