I feel like my veins get SUPER irritated when I dig and then that vein is out of commish for a while. I basically try a few times (not digging) on a vein, then will switch needles and move up the vein a little bit to leave the irritated are alone. Sometimes it works, sometimes it doesn't. For a while I was finding it easier to hit with a 29g 1/2" pick, but then I got this weird suction thing going when I tried to register so I went back to the 30g 3/16" needle and that seemed to fuck up my veins less.
I have horrible veins though. If I was shooting coke I would end up in my hands and feet really quick. Guilty of using the neck though. God, I shudder to think that I used to hit my jugular. I can't imagine it now that I am clean.
On a ramble here, but I miss an easy register and good hit on the first try more than I miss the high or rush sometimes. UGH!