Wear perfume.
Seriously.
I carry miniature perfume in my backpack, and before I sit down for a long study session in the library, I put on some lip gloss and perfume. I also keep the rest of my other perfumes right above my desk and I usually put some on before writing a paper. I don't know why this helps me study better. Maybe it's because it makes me feel more professional and serious. Or maybe because long studying hours can make me feel smelly and gross and it's nice to smell something pretty.
Either way, it's a trick I use to gear up for studying. What's your study secret?