Make a list of all the magic tricks you know how to perform. The list should consist of the title of the trick and also what magic techniques are needed to perform. If trick decks or trick coins are needed, make sure to mark that down.
Scan your list. Chances are, it is very likely to find that there are techniques found in almost all of these tricks, and if you perform all of these tricks, you have a great grasp of how to use these techniques.
Determine which type of trick you want to create. Do you want to make a card trick, a coin trick, or perhaps something involving other magical props.
Do you want to be able to perform the trick with any deck or coin or is this specialized for specific trick decks.
Work backwards. Figure out the end result of the trick and work your way towards the beginning. Just like a screenplay, knowing the end result will help you determine how to get there.
Find new ways to utilize the techniques you know. If you are great at Double Lifting (lifting two cards but presenting as one) find a new and exciting way to use that in the trick.
Double lifting is usually done to pretend you do not know the spectator's card, so perhaps use it in a way that hides or reveals numerous cards. A succession of double lifts instead of just one.
Develop your own presentation style. Coming up with your own trick could consist of using something else already done and presenting it different, or combining tricks.