Here is what Jesus told Nicodemus when Jesus was asked the same question.
Being born again is the only way to have eternal life.
To be born again, you believe and accept that you fall short of God's perfect standard.
Believe ON the work that Jesus has done on YOUR behalf. To believe is to be in agreement with what God says is true and changing your mind about trying to obtain your salvation by your own works.
You believe and accept this truth with your heart and mind completely and fully.
Remember no one puts their hands to the plow and looks back, you are sold out on this truth or you are not. This is what makes your change of mind (repentance) acceptable to God.