im a very experienced user, i smoke alot of salvia. its unlike any other drug, and its extremely powerful when used right. for your first time i would smoke 5x out of a bong or any waterpipe. make sure to keep the lighter on the extract the entire time you inhale, and hold in your hit for around 20 seconds.
if you like what happens, you can move up to 10x or 15x, and eventually try the mindblowing 20x. as for dosages, 3 or 4 hits of 5x and you will be tripping a good amount for a first timer. when you move onto higher extracts, one hit does the job. the reason you should use a bong is because for the salvia to have affect, it must be at very high temperatures and so the lighter must be kept on it the entire time you inhale, this makes the smoke very hot and harsh, so water is very nice to cool it down. since i dont like making very long posts, i will post an experience or two in a minute. oh yea, make sure you have a sitter because you will be 100% disconnected from this reality.