How to Choose a Confirmation Saint
So what are saints?
The first thing to understand is why you are being asked to choose a saint. The saints aren't just dead people that you see in stained glass windows and on holy cards. The Communion of Saints is:
[The] communion of "holy persons" (sancti) in Christ who "died for all," so that what each one does or suffers in and for Christ bears fruit for all. (Catechism of the Catholic Church, 961)
Basically, all of these saints who came before you are part of your extended family. They are those wonderful relatives who are praying for you and rooting for you to get to Heaven.
Why Should I Choose a Confirmation Saint?
So just for a minute think about some uncle that you look up to or a cousin that you really wish you could be like and then imagine that this person has been declared a saint and you could ask him to pray for you! Wouldn't that be great? Well, that's exactly what you get when you choose a Confirmation saint - someone to emulate for his holiness and someone to intercede for you in Heaven.
First of all, don't treat this as a box to check off and pick St Francis just because you have a vague idea about his life.
The first thing you should do is pray. Ask the Holy Spirit for guidance in choosing a saint that will be best for you.
The second thing you should do is some research. Browse a library of patron saints online or get a good book of saints to read. You can get a comprehensive saint dictionary, a book of modern saints, or if you are really ambitious you can get the four volume Butler's Lives of the Saints.
While you are reading about the saints ask yourself why you are drawn to some more than others. Is it because they were courageous in speaking about the Faith? Were they drawn to helping the poor? Did they have an occupation that you are interested in or have a family like yours?
As you start to narrow down the saints you are interested in, think again about the reasons to choose one. Is this someone I look up to and want to emulate? Is this someone who I want to spiritually "have my back"?
When I was trying to choose a patron saint, I ended up choosing Thomas Becket. I was born in England and wanted to find an English saint. After reading about a bunch of English saints I was trying to decide between Thomas More and Thomas Becket. Both were the best friends of Kings named Henry. Both were put into their positions by kings who assumed that they would go along with whatever the king wanted. Both chose the Truth of the Catholic Faith over the power of the world and both were killed for it. Not bad company to keep and a good reminder that the Church and the state have always had a rocky relationship.
Once you have decided on your saint, see if there is a good book just about that particular saint so you can get to know him better. Start asking him for guidance and the courage to take your reception of the sacrament of Confirmation seriously.