When you are not to sure how to dress for a function, how do you figure out what to wear? I think it best to be a bit overdressed than being too casual. Last spring I attended a luncheon type affair where men were all in either suits or sport coats, and most wore ties. most of women were in dresses like more basic daytime dresses with heeled pumps, or heeled sandals. There were a few dressy trousers, some blazers, and a few drapey cardis, etc. One young woman-like late 20's came in a very nice outfit, drapey blazer, heeled sandal booties, and jeans-regular blue denim skinnies. I wore a pencil skirt, silky t and a blazer, with heeled pumps. Do you find blazers or jackets more dressy than cardigans?

I feel that unless an invitation states casual, or I am sure it is going to be quite casual one probably should not wear jeans. However this does not rule out black ones if the top one is wearing covers the back pockets. Good black jeans worn like this can be quite versatile IMO.