If it were easy to answer there would be more wearable designs than we have already. To my mind you need to start with a cut that works with the body not against it. Crucially, a designer has to cut for real women. One of the reasons I love Dolce and Gabbana so much. They make every attempt to flatter your curves even if their designs are perhaps tending to the classic rather than the futuristic. Fashion fantastic, not fashion forward as I would say. The cut is mostly everything.
Related to the pattern / cut, you have to think about the way a dress moves. OK, a designer like Dolce and Gabbana will often include elastane in fabrics but that doesn’t mean you have to wear the dress skin tight. And in terms of flattering your body this is perhaps not the best option anyway. A great dress should move. Even if just a tad.
Mentioning elastane brings me on to fabric and pattern. I have said it before but I will say it again, Dolce and Gabbana’s stretch silk is hard to beat. It’s wearable, flattering and comfortable. The whole nine yards. There are exceptions (see my stunning orange Dolce and Gabbana dress as one exception) but I also think the best fabrics carry some weight. This generally means they are more flattering. Only thin women get away with light weight fabrics but most (not all) good quality fabrics carry some weight.
Pattern if there is one should not be overlooked. Pattern and movement are closely linked. Patterns are not for everyone. Smaller frames and thinner bodies should generally pic smaller repeat patterns to turn a good dress in to great (for them) and everyone else can enjoy larger repeat patterns. But any size of pattern should look comfortable on the body.
Another thing to mention is sizes. Typically Dolce and Gabbana mainline are quite generously sized. There are exceptions. But as a rule of thumb you can confidently shop your size. Why is this important? It’s not just a question of ego but rather is a question of ‘fit’. I do try to point out when dresses run small or large. It happens. But mostly you should shop your size if you are looking for a great dress.