The thing I always tell my students is don't count down. "alright sir/ma'am, big poke in 3...2...1...*pt flinches*...miss. Just do "alright sir/ma'am/*insert name here*, big poke" Boom goes the dynamite.
Don't look, feel.
Just like any other skill it takes repetitions, they don't take as long to get good at as you'd think though.
A firm scrub with a prep can do wonders to help engorge a vein.
Bevel up. I hear all this stuff about bevel down on old people, tried it and it doesn't work for me but everyone has things that do and don't work for them.
Once you get a flash, drop your angle and advance a touch more, just cause the needle is in doesn't mean the cath is too, you need to go a bit further to make sure you aren't trying to tear through the side of the vein with a blunt plastic tube. Hold the flash chamber with the hand you started it with and use your thumb and index finger to advance the cath. Maybe it's just me but whenever I try to do the "one handed flick" I blow the line.
If you meet resistance don't force it, back up a touch and try to float it past the valve or pull the cath back and try to advance the needle through the valve.
Be quick about it, the quicker and more decisive you are with the stick the less likely the vein is to roll away from you, is less painful for the pt and, for me, has a higher first stick success rate.
Traction, traction, traction!
I've never bothered with the bilateral IVs either. Our ambulances are set up with the stretcher off to one side so its a pain to comfortably/safely access the right arm sometimes.
I've gotten torn a new one by the Trauma Team for not having two lines on sick traumas. I mean, if you can't get it you can't get it but if you don't even try it's not pretty. We have access to both sides of the stretcher though.
For us large bore lines are 18g or larger. Generally use 16s over 14s though. My go to cath is an 18g. Our ERs prefer them over 20s because they can draw off of them, 20s usually draw unless you get lucky. Yes, I know about hemolysis but that's not what this thread is about.