I currently have my own guild which i created about a month and a half ago, and it is level 14. looking through the activity contribution it's basically me holding 4/5 of the top spots by a mile, along with my friend i do 5s with, followed by a few random people i got in, and then another set of 4 characters i leveled to 85 just last week. Typically unless your planning on running guild events (raiding rbgs ect) your only going to target lower levels to join your guild, but having low levels doesn't level a guild, as the stuff they do doesn't contribute much to the cap every day, and odds are you wont be able to recruit enough low levels to make up that difference. Honestly for me I try to at least get the cap to 50% every day no matter what. The best ways to do this is probably through arena, normally ill just play games with myself and it doesn't take more than an hour to get at least 50% done. Dungeons are a good alternative as well and definitely worth doing at least 7 each week. As a last resort, i have seen people on my server hiring people to get the cap on their guild (some on a daily basis and some on weekly), which honestly if you have the money, but not the time it isn't a bad way to level it.