Thank you's are always appropriate. Take some time to thank God today for the gifts he's given you that have made a big difference in your life. It can be very simple, like:
Dear Father,
I'd just like to thank you for _________________________________.
And my sincerest thanks for __________________________________.
Most of all, dear Father, I thank you for ____________________________.
For these things and easily a thousand others, I offer this prayer of gratitude.
Love,
Dave