Which sites are you using? I find abdomen and side butt least prone to bruising, whereas front of thigh and upper arm often bruise for me (I can't always use the easy sites though, or I get hardening, so I try and at least reserve the more sensitive areas for the smaller doses).
Obviously changing needles every time and having good needles matters.
Also, are you happy with the needle length your using? Too long and you hit muscle too easily, too short and you don't get all the way through the dermis, which is also painful.
You can also adjust the pressure you use a bit depending on the fat thickness at the site you use.
I often roll the skin around a bit between my fingers when picking an exact spot, to gauge the thickness and make sure it's not at all sore or hard from previous injections.
I just calculated, and I've given myself in the region of 80,000 injections at this point. I feel I've got pretty good at it by now, and it's usually painless and problem free, but still can't avoid hitting the wrong spot and getting blood or bruising once in a while.
