^your veins are a lot more likely to roll around and cause you issues, at least for me it does. I find the biggest thing is to go slow, breathe deep and do anything but rush. (im a meth user though, so i wont have w/ds to worry about; and the common rhetoric "if youre shaking too much to hit you dont need one")
I feel really comfortable sitting in a chair with a armrest and kinda rest the site im intending to use on either the armrest or on my lap, and even standing up as long as i can rest the site on something, and then rest the hand that is working the needle on the area near the site. I always make sure that everything feels very comfortable and easy to use, and then i poke through to the vein with a shallow angle, and register whilst keeping my eye on the needle itself, and not allowing it to move. i usually plunge alot slower than im sure most people do, so long as you get your water/dope ratio where you like it there wont be a large amount of liquid anyways. all in all, it can take me over a hour to get a hit because im over careful, but at the same time ive only missed one time too so i think taking it slow is best.