What do you mean by "gimmicks" and "tired"? Sorry for all the questions.
gimmicks means editing the deck to preform a trick, like glueing cards together to make an extra-thick card so that you can find it, or cutting a hole in the deck to hide something.
when cards are tired or "gunked up", they may have lost their finish that keeps them slick, or some are bent from too much springing. also, use old card decks that gat too hard too handle, like clumping in a fan, to practice throwing cards!
P.S. the whole reson these forums exist is so that magicians can gat advice! dont be afraid to ask questions here we all want to help!