Just thought I would share the St. Michael prayer that I say every day. He's not a Guardian angel in the way we think of them, but he is the guardian and defender of God's people! He is powerful! There are many versions of this prayer, with slightly different words, but they all say the same thing:

St. Michael, the Archangel,defend us in the battle
Be our protection against the wickedness and snares of the devil
May God rebuke him, we humbly pray
And do thou, oh Prince of the Heavenly Host,
By the power of God,
Thrust into hell, satan and all the evil spirits
Who prowl about the world, seeking the ruin of souls

If I'm praying for a particular person who is battling evil, I will use their name at the end - "seeking the ruin of Bob's soul"

I learned recently that St. Raphael's (another archangel) name means "medicine of God". I now call on him when someone has a health issue. These angels never work outside of God's will and He created them to help us, so why not ask them to do what they were created to do?