Plan your routine before ever leaving the house. Whether by list or memorization, make sure you know exactly what you are going to do, and when you plan on doing it.
Make sure that the appearance of your gaff deck cards match those of your regular decks. They need to be identical to be believable.
Feel your crowd out. If they seem hostile, scrap using gaff decks. They will search for flaws to point out or the "how to" aspect of your tricks.
Use the gaff deck sparingly. If used too much, people will begin to notice your deck has a plethora of different or "freaky" cards.
Never start or end with a gaff deck trick. You can do these gaff tricks in a performance of 10 tricks, but never start or end with them. You always want the opener and closer to be done with real cards.
Blatantly point out the realness of your regular decks when using them. Since they are identical to your gaff decks, and your misdirection points out how real the decks look.