If you really think about it, you are being a total douche when you pray for anything
You are basically telling god... that you know what is best, more than god does
By praying, you are saying...
"Hey god, I know you don't want to give me a new car, but I want it anyway"
"Screw your perfect/divine plan god, I want a new car... me me me me me me, it's all about me"
If it is god's will... why are you trying to change god's will?
Do you really think you know better than god does?
Or, are people just selfish and don't care what god has planned?
I think it depends on what you believe in. If you believe that God has a plan, you will not put your needs and wants on your prayer. Usually other people say their prayer to thank God and to forgive them for their sins. I think you can just add up you wish and let God do his plan. If he thinks that your wish is up to his plan then he will surely grant it in his plan. There's no format for prayers, prayer is your way of speaking to God. Your prayer depends on how you view God.