I usually have a rough time donating blood and being nervous about it, but I still donate blood regularly. Here are my tips and tricks!
1. Be sure to eat a decent meal and drink lots of water beforehand! A good meal will help prevent passing out and drinking lots of water will make it go faster.
2. Bring a distraction, like your phone or a magazine or a book. Even though it only takes like 10 minutes (at the most!) keeping yourself distracted will help keep away nerves.
3. Tell your person you're nervous. They'll keep a closer eye on you and can help calm you down. I usually have my person tilt me back a little and/or put some ice on the back of my neck.
4. Breathe and relax. I have the tendency to tense up and hold my breath without noticing it, so I focus on breathing.
Hope this helps, but I'm sure you'll do great! Donating blood is something I'm pretty passionate about, so it makes me happy when people do it! Let us know how it goes! :)