The most powerful prayer in the world is one you can pray anytime.
Jesus was asked by his disciples to teach them how to pray. This is the prayer he gave us.
Matthew 6:9-13 "After this manner therefore pray ye:
Our Father which art in heaven, Hallowed be thy name.
Thy kingdom come.
Thy will be done in earth, as it is in heaven.
Give us this day our daily bread.
And forgive us our debts, as we forgive our debtors.
And lead us not into temptation, but deliver us from evil:
For thine is the kingdom, and the power, and the glory, forever. Amen."

When you look at this prayer you will see several things:
First we pray to God the Father, the creator of heaven and earth.
We pray to a Holy God, with respect, as he is almighty.
We are to pray for Him to be the Ruler of all men on earth.
We should pray for God's will to be done in our society and personal life.
We are to ask only for the needs of one day at a time, our daily bread.
We ask forgiveness from God on the same level as we are willing to forgive others who owe us money or forgiveness.
We should ask for God to lead us in our daily life, so we do not get into wrong company, and be tempted to do wrong.
We acknowledge that God is in Control of everything, and we are willing to obey Him.

Remember, it is not the prayer that we pray that changes things, it is the God we pray to who changes things for us, if we trust in him.