Are you tying off? Are you staying hydrated? Where are you trying to hit yourself? Do you fully understand the consequences on going down this road?
You want to go in on a shallow angle, you're not trying to dive bomb your vein. Also, pull the skin tight below where you want the injection site to be. This should eliminate the "rolly vein" effect. If you see the flash of blood but still feel the needle "missing" your angle is fucked and redo it. I learned like this, you're landing a plane not stabbing someone. It'll take practice if this is how you want to go. I practiced with just water to get my technique down, if you can help it and please do make the investment, use fresh rigs.. Don't reuse them, they will wreck your shit and track marks are a motherfucker to get rid of it, if you can get rid of them at all. There's some online guides used for nurses and emts about proper IV techniques. Google them you'll get the idea
Be safe man.. this shit is serious