If you confess with your mouth that Jesus is Lord and believe in your heart that God raised Him from the dead, you will be saved.
Now lets look at something else here.
I believe first and formost Christians should be out winning lost souls to Jesus, yet we need to be carefull not to sell worthless fire insurance.
When ever i have had joy of eing used by God to help a lost soul find it's way home I allways have them pray to God out of their own words. I tell them to just talk to God, to in their own words to ask for forgiveness and to ask for His help to live for Him. This way it is from their heart and not just some repeted words that really don't mean something. Now I am not saying that a sinners prayer is wrong or that people have not been saved this way.