find a pen or someshit that you can make a one hitter out of. (by one hitter, I mean a pipe you can rip the shit out of, and kill it, in one hit)
Then, squat down like this
After being in this position and breathing normally for about 4 or 5 minutes, get your pipe packed with all your weed ready.
Breathe in and out (deep breaths) for about 5-10 seconds. This is to over-oxygenate(probably made that word up) your blood which will help you hold the hit in longer..
After you've done that, and are still in the squatting position, put the pipe to your mouth...
Now, light the pipe and take the biggest hit you can. Try to cash it out on the first hit. right after you either cash out the weed (and begin to suck air through the pipe) or right after the weed stops burning, take the pipe away from your mouth.
Immediately after taking the pipe away from your mouth (which should have been done immediately after you stop inhaling smoke form it), open your mouth and take a huge gulp of fresh air(enough to fill up your lungs), while at the same time, standing up fast. You should close your mouth right after you stand up and try really hard to hold the hit in (even if you don't need to try very hard.)
Now, I would recommend doing this in the grass and not around anything hard because I have passed out before while doing this. If you do it right, you will be fucked up like you huffed those cans of compressed air, but only for like 10 seconds. If you do it right, you should get a crazy big head rush like when you get up too fast but coupling it with the weed makes for a nice few seconds. Hold the hit in as long as you can, this is important so that you make sure you get the full affect of however much you inhaled. And if you wanna stop the feeling, simply exhale and take a deep breath.
I hope I explained it well enough, if you have any questions, just ask...