There’s no substitute for George R. from the CAT/CR at Children’s Hospital Boston, he has vast experience in finding veins, he made Andy happy and made his IVIG infusions as “easy as pie”.
Here’s something that may help the others.
The ‘vein entry indicator device’ beeps when the IV needle finds the vein.

Developed by an Israeli company Vascular Technologies Ltd.
The electronic gadget makes a sound within 0.1 seconds of the needle’s entrance into the vein’s lumen.
Company website here (the website also beeps).