If God already knows our needs, then why does He want us to pray to Him? I believe that it's somewhat summed up in what we call "The Lord's Prayer" in Matthew 6:9-13.
10 Thy kingdom come, Thy will be done in earth, as it is in heaven.
11 Give us this day our daily bread.
12 And forgive us our debts, as we forgive our debtors.
13 And lead us not into temptation, but deliver us from evil: For Thine is the kingdom, and the power, and the glory, for ever. Amen.
As Christians, He is our heavenly Father. We are to reverence His holy name and never blaspheme it. He desires to commune with His children. We should take the time to go some place where we can be alone and just spend it with Him in prayer and reading His Word. Magnify Him as Father!
King - "Thy kingdom come, Thy will be done in earth, as it is in heaven."
He is the King of the universe! He is omnipotent - He has unlimited power! Let's pray for the advancement of His kingdom and for His perfect will to be accomplished. He is in control! Magnify Him as King!
Provider - "Give us this day our daily bread."
God the Son came to this earth to serve (Matthew 20:28). He delights in serving His people. This is shown in Matthew 20:30-34. On His way to Jerusalem, He heard two blind men calling for Him so He, the Creator of the Universe, stopped to ask His own creation, "What will ye that I shall do unto you?" They asked for sight and He compassionately gave it. He wants us to depend on Him alone. We must always keep in mind that we need Him and that all good things that we have are from Him (James 1:17). Magnify Him as Provider!
Forgiver - "And forgive us our debts, as we forgive our debtors."
God is faithful and will forgive us of our sins if we confess and truly ask for forgiveness (1 John 1:9). Just as we want Him to forgive us, so should we forgive others. Why should we hold grudges and not forgive others when we repeatedly sin against God yet He is patient and kindly tolerates and forgives us? How wonderful it is to have a forgiving God! Magnify Him as Forgiver!
Deliverer - "And lead us not into temptation, but deliver us from evil"
God doesn't tempt us (James 1:13-14) but sometimes He allows us to be tempted, yet He promises that He won't tempt us above what we're able to endure and He'll always make a way of escape (1 Corinthians 10:31). Let's pray for Him to deliver us from the evils of this world, so that we're not influenced by them. Praise God that we already have the promise that Christ will deliver us from this world ruled by Satan (Galatians 1:4). The Old Testament really demonstrates His delivering power by Him rescuing the Israelites from Egypt. Magnify Him as Deliverer!
"For Thine is the kingdom, and the power, and the glory, for ever. Amen."
This doxology at the end of the prayer brings even more glory to God. He is the glorious and powerful King! Prayer is yet another way to glorify Him! Why pray? To glorify God by obeying His command and meditating on His attributes. Magnify Him as Father, King, Provider, Forgiver, and Deliverer! Magnify Him as the "Alpha and Omega, the beginning and the ending...which is, and which was, and which is to come, the Almighty" (Revelation 1:8).
"Prayer is the shield to the soul, a delight to God, and a scourge to Satan." ~John Bunyan