I would guess about 1/4 of the time I get some blood. Most times a drop or so, rarely a good squirt. Though I do try to not stick myself where I see veins or capillaries, you don't really know what is under the surface. You nick or go right through something and blood squirts out after the needle is removed.
What is key is aspritating, or pulling back a bit on the plunger to make sure the needle is not in a vein. If blood appears in the syringe, that is bad. Also try not to push or pull as you inject since there is no way of knowing what changed down there. Much easier said then done when you are doing it to yourself
What bothers me far worse then blood is seeing the elixir of life bubbling out as I try to put on a band-aid. I paid good money for that stuff! I want it all!