A few tips from someone who's been battling tolerance for years:
Try smoking less during each session, and don't redose (smoke more) at all or until you've almost completely come down from the last time.
Find different (and better) strains. Many strains seem to have a ceiling, in other words you can smoke more and more of that strain without getting higher than a certain point.
Better strains generally have a higher "ceiling," and switching up strains is extremely useful in keeping tolerance low (or at least in getting higher). A certain amount of tolerance seems to be "strain-specific" so you may think you have a very high tolerance, but it's possible that a different strain could still get you very high.
Also, get better weed, if possible. That may sound like i'm making an assumption that your bud isn't high quality, but I obviously have no idea what your stuff is like. That said, you might be surprised to find that there is better shit around. Keep your ear to the ground.
And as others have said, take a break. That's the only real way to lower your tolerance, as far as I know. A break can also be refreshing mentally/psychologically, and will also help you appreciate the high again when you start again. A week break will probably give you a pretty couple intense highs when you come back. Two weeks or more and you'll feel almost like you'd never smoked before. There was actually a study done on rats (which may have limited applicability to humans) with cannabis tolerance and I think the conclusion was that about 11-14 days was required for tolerance to disappear (sorry not to cite a reference, shouldn't be hard to find the article if someone is so inclined). The above tips are just "tricks" to stay high, but won't necessarily actually have any impact on your tolerance.
Good luck.
