Praying is the way we show acceptance of God. Jesus said (in Matthew chapter 6) that praying is not to be done to show others how holy you are. He suggested, rather, that you pray in private and when you do you pray like:
Our Father in heaven, hallowed be your name, your kingdom come, your will be done, on earth as it is in heaven.
Give us today our daily bread. And forgive us our debts, as we also have forgiven our debtors.
And lead us not into temptation, but deliver us from the evil.
This prayer does a number of things. It acknowledges the One (obviously you believe if you are praying to Him), it acknowledges His holiness and it acknowledges your subservience to His wishes and plans. It then goes on to you, as the petitioner, for God to provide what you are asking for. And even then it shows you are not just asking for hand-outs. Asking for forgiveness of your debts has the caveat of as we forgive others. In other words, if you aren’t following the rules, you will get treated as you treat others.
Does God know all your needs? Yep. Just because he knows them, you have your role to play. And just because you want something and pray about it, sometimes the answer is no. Just like with being a good parent: you know what your children need. You provide for them to help them be the best adults they can be…to be quality human beings. But your kids will come to you telling you all the things they “need”. Some of those things might be needs (I’m outgrowing my shoes) but others might not be (I need the new iPhone). It is your decision as the parent to give them what they need but not spoil them.