Need some advice on blood draws

Here lately when I draw blood, I've been having trouble hitting the veins that are deeper, and on people with bigger arms. I've even missed on patients that I can usually get. I don't know what I'm doing wrong. Any advice would be appreciated. Thanks!
Maybe you are going in too fast? That was my biggest problem because I wanted to make it painless for the patient but it's counterproductive because I would go fast the vein would move or I would miss it and have to poke again Also anchor the vein tight with your hand so it won't move. I also find putting the arm band around their arm having the vein pop up then untie it clean the site prepare etc then re tie it.A lot if people I know will look for the marks where blood has been taken before and just go above that dot. You will get it it just takes practice