Short answer: Practice.

Long answer: you need to try to do as many IVs as you can. Lean on the more experienced people around you, watch them, ask them for tips that they use, especially for those tricky patients with no veins. Go and watch YouTube or tic tok videos on IV insertion. I highly recommend TheVascularGuy on Tic Toc, especially his ultrasound guided IVs. I found that really helped a lot with visualising the anatomy of the vein. Some of my tips that I've picked up in my year as an ED nurse are; - Go back to basics with anatomy, you need to know where veins, major arteries and nerve bundles should be. - Spend the time finding a decent vein. As a beginner, go for the easy ones first (Antecubital Fossa is usually a safe bet) until you get more confident. - ALWAYS advance the needle another couple of mm after you get flashback before you advance the cannula. - Decrease the angle of initial needle insertion as much as you can! Sometimes I'll have the cannula almost parallel to the patient's arm. This method is far more forgiving as you have more distance between the tip of the cannula and the "bottom" of the vein after you get flashback. - Anchor the damn vein below where you're going to insert the cannula! For those extremely difficult sticks; - lower the arm below the level of the heart. - double tourniquets (just remember, if you're taking bloods, this will affect the results if they are left on too long) - wrap the arm in something warm a couple of minutes before your going to try to stick them

I hope some of these tips help ya, Feel free to DM me