Heres how our IV training went.
Instructor calls me to the front and every one gathers around. Sits me down and rolls my sleve and demos a 'stick' then every one had to do it on the dummy arm once (With out the koolaid)
Then we each had to get 10 'sticks' with an instructor hovvering over our shoulder. Once she was satisfied with our technique, she would pass us and we were cleared to do IVs in the fields on clinicals. TN only requires 5 perfect sticks in the feild, but my instructor wanted us to have at least 10 in a moving bus, and 10 in the ER.
I winded up turning in 49 sticks by the time my clinicals were over.
Practice on a human imo is the only way you can get good at it.