I wouldn't drink coffee...caffeine is a vasoconstrictor AND a diuretic. So it will dehydrate you and make your veins even more difficult to find. Elevated blood pressure doesn't make it easier to start an IV. My husband has high blood pressure and he drinks a ton of coffee...and he is a very hard stick most days (twice he has had emergency visits to the hospital and the ER nurses took two tries to get an IV started on him...because he is chronically dehydrated).
Some facilities have machines that help find veins, but many do not. Many hospitals have an IV team that specializes in starting or restarting IVs on patients the floor nurses are not able to get. Perhaps when you go in, in addition to being well hydrated and using heat to dilate your veins, you could let them know you are a hard stick and ask if an IV team is available.
There is an easy way to pick out veins. I discovered it in the army forty years ago testing third generation night vision devices, but unfortunately did not file a patent. The technique is actually public domain, although a recent patent has been issued because it was submitted to the Army medical department as a suggestion it is invalid as the method is public domain because the DOD was advised ot its utility over thirty years ago.. A simple thermal imaging unit will pick up all the veins, which are then outlined with a marker.
I don't buy the prescription of xanax at all because it causes loss of muscle tone.
Two hours before the examination drink a cup of coffee. An hour before drink another cup. Within two hours consume 32 ounces of fluid. An hour before drink a glass of water with a half teaspoon of salt. Jog for a few minutes before the exam. These will all serve to raise your blood pressure and more clearly define the veins. Before the exam "swing" your arm.
Lastly, ask for a more experienced tech. It's an art, not a science. You are being fed a tiny bit of nonsense to cover up for inexperience of the tech. Then again, what else are they goinhg to say? I used to always get the veins that nobody else could.
Do drink lots of water until time is up. You want to be well hydrated.
Then remind yourself this is just mind over matter as far as the needle stick. It really is just our brain over-reacting. I do this with bugs that move fast. Some people do it with snakes or rodents, and other people do it with being stuck.
If you try to be very blase about it and tell yourself it is no big deal, it will actually help you. It is very important to practice slow deep breaths where you make your rib cage move. This actually tricks the brain and body into thinking you are relaxed.
Just don't get up fast. The worst that can happen is that you might feel faint really.
Drink as much water as you can hold the day before. The better hydrated you are, the better. I used to donate plasma and drinking the day before (day of helps also but day before helps more).
Other things that will help...about 10 minutes or so before they are going to try to start your IV, make sure you keep your arm down...hand pointing toward floor, arm straight....see if they can apply warm towels or a heating pad to your arm...don't do it too long before they are going to start...10-15 minutes is best