I always find it helpful to see the process that others go through to get to the perfect fit, so I thought I'd share a bit of my process. Of course, the disclaimer need be said - this is the way I do it, not the only or even the best way, so I'd love any input about your personal fit journey and what works for you.
FFRP, and I HATE making muslins, so I do most of my fitting on the pattern tissue. I'm also an inveterate tracer, so all of my patterns are traced onto soil separator fabric before I start. The great thing about that is that I can just baste together my main pattern pieces and go from there. The above image is the front of my dress, without sleeves, collar, pocket, cuffs and facings. This pattern is cup sized, so I didn't have to do an FBA. I cut a size 10 with the D cup front and blended out to a 12 at the waist and down to the hem. As you can see, the fit is pretty good!
I think I'm ready to cut fabric!
ETA: Karin asked about the soil separator fabric that I use for tracing. I meant to talk a little about it because I LOVE IT! It is a plumbing product that is used in septic systems. In the states, you can get it at some hardware stores, although my local shops don't carry it, so I order it online. The kind I am using right now is made by Hancor. I order it from amazon.com, where it is called "geotextile fabric". I love this stuff for many reasons - it is sheer enough to easily see your pattern through, but sturdy enough to go through multiple uses. It drapes and can be sewn like fabric. And at 25 dollars for a 100 yard roll, it is about the cheapest tracing medium you can find. I have also used it as stabilizer for embroidery/applique and it works as a lightweight sew in interfacing. Brilliant!