Prayer is asking God for His attention to a specific matter. Yes, God knows everything, but He wants us to ask Him so He may be glorified.
Also, God has a plan. He knows what we need, which is eternal rescue from Hell( the place where you will spend eternity burning in unquenchable flames) and a ticket to Heaven( the place of eternal glory, where every single aspect of life is completely perfect). It would be better for you to die and to know Jesus as your personal Savior because of no material goods( going to heaven) than it would be if you lived for a good while on material goods, and you died not knowing Jesus as your personal Savior( going to hell). Finally, humanity has no credit due to us. God created us, gave us free will, and gave us the option to heaven. God works through saved and unsaved people to bring people closer to Him. We, humanity, have not done anything that God did not want us to do. He directs us, and we serve Him.
Praying is an attempt to take credit without actually contributing. Even worse is I suspect many will say "I will pray for you" and then don't follow through. Not only could they not be bothered to contribute, they could not even be bothered to mumble to themselves for a minute.
Let me further expound on what Morganic said. I don't know what you're praying for, but assuming you live in a first-world country in which Christianity is the dominant religion, you believe that God "loves" you along with the rest of humanity. Assuming that you believe that god is omniscient, omnipotent, omnipresent, and omnibenevolent (all-knowing, all-powerful, everywhere at all times, and all good), then you must accept that God knows everything that will ever happen before it happens. He has the power to do anything he wants. Your prayers would be useless, because god is going to do what he wants no matter what you ask of him. He also knows what you're going to ask before you ask it.
If your prayer is of a spiritual nature (love, happiness, fulfillment, community, family, etc) then prayer might be useful. On the other hand, if it is of a material nature (money, house, car, new shoes, etc) then you're on your own. If he won't help the majority of the poverty-stricken world obtain material goods, then why would he you? Because you're a better Christian? What of those who've never even heard of Christianity? Are you his favorite?
If it's a medical cure, go to a doctor.
Some people even believe that god works through them. Why not cut out the middle-man and give humanity the credit it's due?
There is no evidence that prayer has any effect, if it did there would be a lot less people dying of starvation, I am an atheist so of course I'm going to say no, however if you do believe why do you think your God would help you if you're not prepared to help yourself?
Okay if there is a God, what i don't think that there is, he has a divine plan that only he can know right, that doesn't change, so praying for him to do something is pointless, he is going what he has choose anyway I don't think the all knowing God is going to change because you know something he doesn't.
Before praying you must carry through on your own before praying. You can't leave your car unlocked in a parking lot and rely on God to keep thieves away just like that. You must do your part before asking God for reliance. If you are sick, go to doctor first then pray if nothing else can be done. God then will listen to your prayers. He doesn't want you to be lazy.
The reason I put my answer on the neg part because praying is not better than doing it yourself but it is equal. Praying is as important as doing it yourself, but prayer doesn't always help because God sometimes doesn't want something to happen for the best of you. God is more knowing than the human and you may be asking for something that can harm you, but you just don't see it.
So in conclusion, don't be lazy and just fix your problems.