Basic Christianity, you want advice talk to your minister.
If you are seeking to serve God you will already helping in your church, and learning more about Christianity.
Your leaders will have seen you working and will have an idea of your capabilities so will be able to advise you.
You don't say what the charity work is, again your minister will be aware of the charity and will be able to give you advise and even recommend you.
However, if you don't belong to a church, rather than doing charity work, make finding a church that can help you grow as a Christian your top priority.