Despite patient and doctor following all precautions, some people are simply more likely than others to bruise after filler.
To to reduce the risk, you can stop all blood thinners 7-10 days before. These include aspirin, ibuprofen, Motrin, Naproxen, fish oil, vitamin E, omega 3 fatty acids (and many more you can find on google). Also don’t drink alcohol a day or two before. Patients with a history of easy bruising can take Arnica a day or two ahead of time and continue it for a few days after injection.
Your doctor can provide you with ice to use before and after injection, use a small/frequently changed needle, and hold compression over the injection sites.
After the procedure, you can continue to use cold compresses to minimize bruising and swelling. You can use Arnica pills or topical gel if bruising does occur.