Even with a dress dummy I find I still need to make adjustments, as the dummy is not exactly my shape.
I almost always make a muslin if I'm working from a design or pattern (as opposed to refashioning existing garments) and then make adjustments to that with the pinching and pinning. Sometimes you can't reach the area that needs to be pinned, like at the back, so you'll have to kind of eyeball it while it's on you, making mental notes or even real notes about what needs to be fitted, and then take it off and pin or basti where you think it needs to change, and then try it on again. Eventually as Aislynn says you'll get used to seeing what needs to change, and you'll be able to fit more quickly. I usually take forever to make anything, anyway....
Making a muslin and using it to make a permanent pattern which you know fits can save a lot of time if you intend to make similar garments repeatedly. "Real" seamstresses
work from whats called a "sloper" which is based on your own measurements and can be adapted to other patterns. Learning to make your own patterns is a whole fascinating challenging endeavor but can save a ton of money. I haven't bought patterns in years (maybe a decade).