Pick one faith and stay with it. Dilettantism is the mark of the amateur. Avoid needless embarrassment. Practice the correct pronunciation of your deity's name in the privacy of your own room before chanting it in public.
Flash cards are often helpful.
Never invoke anything bigger than your head. Citronella candles may not be used in rituals. Pastel-colored candles in the shapes of cute animals are like beacons to the Powers of Darkness. Ransacking hotel rooms is probably safe, but going 'round to beat up the good guys is a sure route to the bottom of the Thames. When the Black Mass goes awry, stay away from the Evil Priest.