The three critical things you need to know in order to be a good priest, as said by a good friend who just happens to be a deacon and almost a priest:

1)  Love Jesus.  By this, I mean that you should think of Jesus as your best friend and closest, most intimate relationship in your life.  Everything you do for others, know that you are doing the same for Him.  Jesus is not an abstract person who happens to be God, but Jesus is our Savior who sacrificed His life so that we might have life.  This is most important.

2)  Be faithful to His Church.  If the church teaches something, you need to realize that His Holiness Pope Benedict XVI and all other cardinals, bishops, etc. know way more about the subject than we do, and if we dont like something they teach, to realize they proclaim it because they know and want whats best for us and that Jesus taught it, too.

3)  Be Holy.  Don't try to fit in with the worldly crowd, but be set apart and set your life apart for Jesus, your Bridegroom.  Sanctify yourself and save yourself for Him, so that, when you meet St. Peter at the Pearly Gates, you may appear Pure and Stainless, so you can enter the Kingdom of Heaven.

Well, I'm new at this, so have mercy on me.  Let me know what I should talk about on here!