I am always trying to improve myself deep down, so I let the fact that there are people who are better than me motivate me. I think, "they're amazing, I want to be even MORE amazing than they are!" This is what has always pushed me to be a better athlete, musician, gamer, and scholar.
Also for motivation in general, having deadlines...and being afraid to not meet those deadlines and what the consequences will be (hearing it from my advisor, bad grade, etc) Setting little deadlines, ex. I want to have A done by this time, B done by this point, and reach point C by then always helps me actually get things done.