I cap flags. Dont waste time, get out there quick (buy your item before choosing your skill and favor item, those 2 can be done while you are moving) and capture a flag. The flag capture and some times one or 2 creep deaths near you is all it takes to hit level 2. Kill the rest of the wave, head to another flag (preferably one in a creep lane).
Thats the tactic, the variable is enemy DG's. Play accordingly. Stay safe, harass when you can. While flags are always worth good experience, once you get to levels 4 and 5, it becomes less important and you can stop grabbing flags for expereince purposes. Which is to say, do your best to keep control of the flags, but no longer take the experience gain into consideration when choosing what to do.
This is the tactic you spoke of, where your oponents are level 4 while you are just coming up to level 2.
Hope it helps!
(PS: A little note about Karma. You need to click the little thumbs up button below this post if you want to give it to me. Giving it will cause more people to take my advice seriously. If it helped you, do others the favor and let them know its good advice!)