The best way to find good quality is to check the garment tag: What kind of material is it made of? Jersey 100% cotton or any 100% cotton is one of the best quality material for most casual clothing.
Then, you should touch it (designer step/touching). You will get better along the way. If you think you will like it, it may be a good quality. You should try it. and look for similar material when shopping. It does not matter the store where you shop, you should check the garment quality because even at the expensive stores you can find bad quality.
Quality in Stitch: you should check the the garment stitch, look at the top and underneath stitches, watch for good and consist stitching pattern. especially the sides and armholes underneath of the garment.
Style is something personal. Everybody has different style, but stores are classified by age targeting. If you can find a store that usually made your style, good quality material at reasonable price. you should consider shop there. Most of the time, it will cost a little bit more or much more. BUT CHEAP IS EXPENSIVE!! you end up spending more money at the end of the year.
Reasonable means a fair price for both parties, You and the seller. Neither cheap or expensive.