I agree with the above poster, NEVER go with a vein you "see"!!!
I took a class as part of my CNA training(and EKG, yadda yadda), and LOVED it. I was always SO nervous about finding a vein(we practiced on each other in class), so as weird as it was at first, I practiced finding veins on anyone I knew. They may have found me a little crazy, but they put up with it, and when I found one and let them feel, they found it kinda cool!
Ultimately though, practice makes perfect, I think.
Also, my teacher would have us "mark" the spot sometimes, mostly in the beginning stages.....I'd use the alcohol wipe that I use to clean the skin. I palpate, and don't move my eyes from the spot, then wipe and put the wipe in a diamond shape(if that makes sense? So a corner is pointing right where the vein is) and that helped me a lot