Don't hold your hits in any longer than a few seconds. Most of the THC is absorbed instantly.

I'm not sure. If pressed I would say that smoking a large amount in a single session as opposed to spreading it out over several days would be slightly more harmful to your lungs, because cannabis is a bronchial dilator, meaning that it opens up the alveoli in your lungs, which may allow tars and carcinogens from the smoke to get in deeper.

Honestly, though, you really shouldn't worry about lung damage from smoking weed unless you're a heavy everyday smoker like me, which I'm assuming you're not. Cannabis smoke, especially when filtered through water (get a bong) is relatively mild.

High-quality weed, dried and cured well, is a much smoother, not to mention tastier smoke than schwag. Plus, of course, you'll have to smoke a lot less to get much higher.

I hope that was helpful.