if you are using a questing profile, any quest you complete will increase your guild rep. update.. i think also that doesn't start till after level 10 or something like that ...
I don't think you understand chaos-dark. What xopherw is saying is that you can use a level 10 profile, regardless of your level, to gain guild rep.
Your options are to group with guild members and run dungeons/raids, or do what has been suggested here and run a quest profile. Guild reputation comes from completing certain quests, and when you do them at level appropriate times you get slightly more rep (ex: 4 instead of 1). It has nothing to do with experience. There is no hands free way to get guild rep other than questing (unless your guild doesn't mind you botting through instances with them). You might not like the answer, but that's the only one you're going to find that is accurate.
Guild reputation comes from completing any quests. Until 80-85 questing profiles become available there's no reliable way to bot guild rep.
try running some of the 58-68 questing profiles .. that should get you started then run through the 70-80 questing profiles ... that is what i have been doing .. good luck !