You have been given some excellent advice. As a nurse of 30yrs and ER experience, I want to go back to basics: Make sure you're comfortable. Sit down, if possible, allow gravity to help you and allow the extremity to hang downward. This will cause some veinous pooling. Keep the ski taught. Start the IV low and slow in a steady forward motion. and most importantly, trust yourself! Don't automatically assume you missed...back the needle up just slightly and reangle slightly upward / downward or more toward the direction the vein is going then advance again. I do a lot of teaching, and these are game changers. NO BODY KNOWS YOUR SKILL SET. Breath and be confident. We all miss some days. YOU GOT THIS.