Often we think God only works using the righteous, and to be honest we too often fall into the trap of thinking "that person canít do that for God, look at his past life" or "look what he has done". But the bible shows us that God carries out his work not always through people who are righteous, but also through ordinary men and the worst of sinners it seems.
Peter for example was just a fisherman, not one who studied scripture, just a fisherman and he became a great man of God. Not only Peter, but Matthew was also far from God shown as he was a tax collector but ended up an obedient disciple of the lord Jesus. Finally, Paul of all people, whom was one to persecute Christians was chosen to carry out the work of the Lord, and brought many to faith. These are just few.
So do not think that from your previous life of sin or from being no one special, that you can only do little for the lord, no not at all, because in Christ we begin a new life, and through Jesus anything is possible.