Are you talking about Lipohypertrophy (Fatty lumps) or keloid style scarring?
If it is Lipo then the massage guns work wonders. Renpho do one via Amazon and, if my gym did not have them, I'd buy one. 5 mins post pinning and 2-3 mins every day should help increase blood flow and minimise the scar tissue from forming. Note, you will still get scar tissue. It is unavoidable. Some people have better healing powers which, as we all realise, get less as we age.
Use the smallest gauge needle to pin yourself. Injecting compounds at a slower rate also help to avoid PIP which may or may not cause or contribute to scar tissue forming.
I use my thighs and my right glute only. I do not pin my left glute as I am kack-handed with my left hand and get back spasms when I rotate and stay in the inject my own butt position!
The compound needs to enter deep muscle tissue at 1 inch approx, that rules out most dibetes use needles which are better for SC injections but... you can quarter each thigh meaning 8x pins per week just make a chart and don't pin the same area twice.
Don't jab yourself in the top of the thigh - ie ... do not sit down and pin yourself as you look down at your leg, it needs to be the side aspect running down the outside of the leg. There are less nerves and less large blood vessels you can hit = less pain and less bleeding.
Hope this helps
PS - I hate pinning myself and often get a colleague to do it. Whilst I get frowns it does help if someone can help you do the odd glute jab (only if they like you tho)!