I know most people don't think you can use tactics in the 100m but it's obvious that Gatlin has better outright speed this season so Bolt has to try something different. Bolt isn't in his best shape but he always has a great finish so I think he needs to stay on Gatlin's shoulder for 80m then pass him in the last 20m. He should forget about running a fast time and just concentrate on out-kicking Gatlin at the end.
I don't think the 100m major championships has ever been won by someone running tactically so Bolt might also be motivated to try to be the first to do it. This would prove that he is not only the fastest sprinter in history, but the most adept too.