The most important thing to do to minimize bruising prior to breast augmentation surgery (or any cosmetic surgery for that matter) is to avoid medications that can cause bleeding. This includes aspirin, ibuprophen (advil, motrin), naproxyn (naprosyn or aleve), and similar drugs. Tylenol is okay to take in small amounts. It's also best to avoid vitamins and other supplements.
I advise my patients to stop taking these medications and supplements for 2 weeks before and for 2 weeks after their surgery. Good nutrition is important both before and after surgery, so I also recommend a healthy diet which will include enough vitamins that supplements should not be necessary.
I have tried both arnica and bromelain supplements with my patients over the years, and really have not found either one to make much difference in swelling or bruising. It is more important to avoid strenuous activity, avoid aspirin-like medications, and also if possible to minimize coughing, vomiting or otherwise raising your blood pressure after surgery. I always prescribe a medication to prevent nausea and vomiting for my patients, as this makes for less bleeding, less bruising, and a much more tolerable recovery.