I offered a few tips here and here. Today, I have more visual examples for you. On the Ideeli sample sale site today is an evening wear section. These are two of the featured dresses.
Right Dress = standard boring mother-of-the-bride dress that frequently gets passed off as evening wear.
But further down on the same page was this PATRA beaded kimono sleeve dress.
As I mentioned in previous modest formal wear tips, neckline and "kneeline" are of utmost importance. Two thumbs up here! At 40.25" it's long enough for nearly everyone. (If it's too long, have a tailor take it up at the waist to avoid ruining that beaded border.) So it's just the shoulders we need to tweak and this dress would be incredibly easy in that regard. Just a little addition to the underlining that any tailor could pull off in their sleep. Any reasonable sewer as well.
Do NOT try to fill in the full sleeve. That would make you look like a crazy bat.