I don't buy many clothes for myself, partly because I don't have a great need. I still wear stuff up to 20 years old in good nick. But:
Petites and other specialist ranges were taken out of store and put on line only. I want to know how things sit on me and try them on.
Stock control is very poor.
Sloppy customer service. Too much faux help in some stores, upselling etc. Some stores under staffed. Staff chatting over customer's head at the tills with little acknowledgement.
Stick to what you do well e.g. M& S, forget high fashion, stick with classic basics. Be the shop where 5 different women can walk in and buy well cut black work trousers/ jeans. Keep it simple and reliable. Improve the bra sizing and fitting (it's surprisingly tough being below 34 back, small cup and the Angel bras are too thin on a fully fledged woman) Too many shops trying to be evetything to everyone and doing it badly.
Sell decent quality. My stuff from the late 90s lasts much better than stuff from the last 5 years. I now get impulse buys in Sainsburys because they have a reasonable life and good price ratio.
Keep layouts simple. Let people see what is on display. Let them walk in a straight line from one end to the other. Make features like changing rooms obvious.
Most of the "shopping psychology" bolleaux is counter productive to a lot of people and off putting because it's stressful.