Casual is the easiest in my opinion because it’s more free to choose different pieces and still look fancy for a social event. If your option is a dress, use it something around the lenght of your knee, you can use colors and the shape have to be confortable, since I don’t know your body type. I think it’s really cute to add a small bow in your hair. Avoid a black look for casual events.
Remember that it’s better to be more formal than less, so don’t be afraid to wear what you already have.
Hope that I helped! :)
P.S.: If you - or any other follower - wants fashion advice or have any question, use it my inbox instead of the fan mail, just because it’s easier for me to answer!