Consider the fabric your using. If your making something more structure, then maybe best use heavier weight fabric like satin. If your going with more drape and flow, then perhaps chiffon maybe better. There are many other fabric maybe used, it all depend design and feel your going for. Whatever fabric you choose, do preshrink the fabric by steaming before cutting because you'll be doing a lot of ironing and steaming later and you don't want the fabric to shrink then.
Creating pattern for your design. You can drape your pattern on the mannequin, draft a pattern on paper, or if your really skilled, you can just draft it right on the fabric. For this particular one, I just used a pattern of bodice I've drafted a while ago for another design.
This is an example of an drape pattern.
This is the drafted bodice pattern I'm going to use.