I recently had a mole removed on my left breast, I had to get quite a large chunk of my skin removed and the scar is about 4cm long. Its been about a month since its been done and I'm really worried about my scarring. Ive had my bellybutton pierced twice and both times the scarring has been pretty bad, I've also had other pretty bad scars that are pink and raised which I've had for years.
Is there any advice to help reduce bad scarring?

You have hypertrophic scarring (as do I, although the doctor 50 years ago called it keloid, but keloids are much worse and spread).
Ask for a very tiny needle cortisone injection, and ask for one any time you have surgery. It makes all the difference. Especially no itching!
Buy some cortisone OTC cream and that should help.
Some people think Vitamin E, either in pills (the natural E, not synthetic, and check the fine print on the label, because a lot of it is called natural but is only a small %) or in cremes.
Vitamins (A is another) and a healthy diet in general.