I think your best bet is to just be calm about it, no need to get worked up, its going to happen regardless... it will also make the person doing the IV more comfortable, which makes things easier as well. Try to hydrate as much as possible the day before, drink double what you normally would in water and avoid caffeine the day before as well. When you do get someone that finds a good vein remember where it is and let the person know that is where someone was able to get you before. Breathe! Dont forget to Breathe! haha. Hope this helps