There are many medications, vitamins and supplements that can put you at an increased risk of bruising and/or bleeding during injectable procedures. A comprehensive list can be obtained through your doctor, but some of the more common ones are Vitamin E, fish oil/omega3 fatty acids, ginkgo biloba, and garlic. Non-steroidal anti-inflammatory medications (NSAIDs) such as aspirin, ibuprofen and naproxen also place you at an increased risk.
There are some injection techniques that can be done to minimize bruising if that is a big concern for you. Your injector could add a little bit of lidocaine with epinephrine to the filler. The epinephrine will tend to constrict blood vessels and reduce bruising. Also, the filler could be injected through a blunt cannula rather than through a sharp needle, which reduces the risk that the needle will lacerate a blood vessel and cause a bruise. Finally, I like to use a topical anesthetic ointment which contains lidocaine and prilocaine. The prilocaine will cause some vasoconstriction/blanching of the skin prior to treatment which may help to reduce the risk of bruising.