Shorts and shirts are standard in our house. Dresses would (I imagine) be a little more difficult. Here is one of the earliest photographs I have of Otis in his care of self - dressing area when he was 13-17 months. The cube chair and sitting has really helped with this process which can begin once they can sit.
I'm not going to pretend that you need help with this. I'm sure everyone knows how to dress their own child. I've actually been told numerous times that helping a child to dress while being behind them is helpful, that way you can place your hands where their hands need to be. It's always made sense to me for Otis to be sitting and it's best with his chair against the wall, so this is how we do it. Otis likes to do most of it himself now and as the child gets older they will need your help less.
Underpants and really all pants can be placed on the floor to start with. When Otis was younger he would stand in the holes, put each foot in each hole - then pull up his pants. Now he is older he will put one foot in one hole, pull up a little then put the next foot in the next hole and pull up.
Shirts can be placed on the floor in front of them or in their laps, Otis can sometimes get this far himself but often has his shirt on back to front. The tag goes at the back Otis.
Teaching him to hold his shirt like this has meant he gets his head through easier. Not easy but easier. It doesn't always work.
Then he needs to find the arm holes.
If this happens I hold/stretch the arm of the shirt out and he can put his arm back in and find the arm hole himself. I don't push him, if he starts to get frustrated I will increase my level of help.
Loose clothing is easier than tight fitting. Younger children can start slowly, by stepping into or putting their feet through the pant leg holes and the parent can pull up the pants. Consistency helps, having your child participate in dressing everyday is best rather than some days you do it and other days you expect them to. Set them up for success with easy clothing. Full them with confidence, don't embarrass or dismiss them for their efforts. Self dressing is a little like toilet learning, I believe the earlier they can do it themselves the better but it's time consuming and takes patience.