Obviously, doing something not-blatantly-unhealthy is probably a good idea; but amphetamines and modafinil are the tools of choice among students these days in need of a performance enhancement.
If Modafinil has any serious downsides, they certainly are subtle ones. Unlike stimulants, which leave you tired but jittery, it just makes you not tired. The amphetamines, of course, are to be treated with respect and moderation(oral doses, ideally sustained release, you aren't trying to get high here); but can, somewhat surprisingly, sharpen the hell out of your focus. Just be careful. In my experience, they Don't improve the targeting of your focus. If they help you maintain intense focus on a piece of work for far longer than would otherwise be possible, great. If they help you maintain intense focus on completing 100% of the achievements in Dishonored, less useful; but they'll do either depending on the situation you put yourself in.