Well do you want a WISH or do you want a SPELL? A wish is in itself its own ritual, leaving a little more up to fate. A spell can be used to obtain something you desire, but I think a "wish spell" is redundant.
If you want to use the Law of Attraction, the steps are:
1.) Ask: Ask the Universe for what you want.
2.) Believe: Believe that you have what you want. Don't focus on 'wanting a car', focus on HAVING the car. You have the car.
3.) Receive: And you will receive what you intend to. Put out energies that will draw that desire to you.
There are many useful tips for using the LoA to get something you want, the most popular is probably the 'dream board/manifestation board' where you put affirmative pictures and sayings that deal with your want; it aids focus and belief.
You can also carry citrine (a type of crystal), which aids in manifesting what you want.
Try creating a spell around the waxing (becoming full) moon, as it represents bring in/gaining things.
Please don't demand spells. Some people on here are willing to aid in creating spells -- some even make them for others -- but please know that your own power is enough.