First of all, take it slooooooooow........this is a skill that requires time, patience, and LOTS of practice to master. And even later down the road when you are more proficient, there will be days when you can't hit the broad side of a barn, let alone a spindly, dehydrated vein with a 24 gauge needle! :chuckle
I subscribe to what I call Zen IV starts: first I collect my thoughts, then go in to visit the patient and tell him what I'm going to do. Only then do I begin prospecting for an appropriate vein; once I find some possibilities, I gather my equipment, turn up the lights, and wash my hands. I usually consider IV starts a sit-down performance, although I've been known to do them practically standing on my head if need be in order to get a line in quickly.
I also bring a Chux to put under the patient's arm to protect the bed linens (pts. on anticoagulants tend to bleed no matter how well you occlude the vein).
If the pt. is a "hard start", or dehydrated, or very large, I'll use a warm moist pack on the prospective site for 10 minutes or so to encourage the veins to come out of hiding. A good vein will be both visible and palpable; it will be plump and elastic to the touch, not rubbery....you'll pick up the "feel" of it as you practice on a variety of subjects. Of course, you'll sometimes have to go by feel alone, and sometimes you'll be deceived by what looks like a great vein but has valves that you'll bump up against and be unable to advance the catheter, or worse, runs away and hides!
Once all is ready---vein and catheter selected, area prepped, tape and transparent dressing opened, IV bag hung and tubing primed etc.---I stick the needle in, bevel up, at a slight angle, depending on the vein (the antecubitals, as well as veins in an obese patient, tend to lie deeper below the skin's surface than, say, those in the hand or wrist), then lower it to where it's almost parallel with the skin surface and advance the needle smoothly until I get good blood return. Once I'm in, I slide the catheter itself further in while at the same time removing the needle.....otherwise, it's too easy to go all the way through the vessel wall and blow the vein. Then I occlude the vein with my non-dominant hand while I attach the tubing and flush solution, take off the tourniquet or BP cuff, and flush to make sure the line is patent. Next comes a strip of tape to keep everything in place, the transparent dressing, and more tape to secure the site and the line. Finally, I start the drip itself and watch the patient for a minute or two to see if he tolerates it well and to catch any trouble before it gets out of hand (yes, you can have what looks like a perfect start, and the next minute you've got infiltration).
Now, it takes longer to tell it than it does to actually DO it.......it usually takes me less than 5 minutes from stepping into the patient's room to documenting the start on the IV flow sheet. But in the beginning, you'll want to take your time, and in the meantime the Intravenous Nurses Society has all the info and helpful hints you could possibly need.......they are THE experts in IV therapy, and they are continually developing new and better standards of care.
I wish you luck. You'll do fine, I'm sure.......just don't get discouraged! It took me six YEARS to finally get comfortable with IV starts---I used to be scared to death, avoided them like the plague, and would always ask another nurse to do them for me if my patient's veins didn't stick up like ropes. But in the PRN position I'm in a lot of times, I could no longer avoid IVs.....and as I did more and more of them, I got to be pretty darn good, and now I'm one of the go-to people for the entire hospital when a hard start comes up. I'm proud of that. And you will be too, once you get past the fear and master this task that is as much an art form as a skill.