Find good lookbooks to derive a sense of good fit and what range of styles exist, how you personally like them, and how the fit in different social contexts. The Permanent Style blog has a bunch on this; the Sartorialist has pictures from a very broad range of styles.
Peruse clothing from high-quality shops and try out a _lot_ of things to get a feel for how clothes fit you and what fabrics you like. Clothing look good because it fits you and goes well with your style and palette and makes you feel comfortable. You'll likely find soon enough that expensive clothes are generally expensive for good reason.
Find a good tailor (or a couple) and develop a simple wardrobe that can be combined easily. From then on be willing to experiment a bit and spend some money trying out a few things a bit further outside your comfort zone.
How does one know what shops are high-quality? I'm sure price is one place to start, but I doubt that all expensive shops are high quality. How do you tell the difference between the two?
Good question. I don't have a general answer; I have a lot of interest in tailoring and formal menswear, where you generally get what you pay for with few exceptions and where you can definitely see the difference in quality of fabrics and fit and finish.
Peruse clothing from high-quality shops and try out a _lot_ of things to get a feel for how clothes fit you and what fabrics you like. Clothing look good because it fits you and goes well with your style and palette and makes you feel comfortable. You'll likely find soon enough that expensive clothes are generally expensive for good reason.
Find a good tailor (or a couple) and develop a simple wardrobe that can be combined easily. From then on be willing to experiment a bit and spend some money trying out a few things a bit further outside your comfort zone.