IMNSHO,the main problem with studying opening theory is that there is TOO much theory,most of it useless crap. As Black,pick out one or two good systems against both 1.e4 and 1.d4,and learn them perfectly. As White,try all purpose systems like the Colle or the KIA,that you can play against all caliber opposition. Cuts down on trying to swot up a lot of theory,most of which you probably won't remember come game time.