I would say where to start depends on where you?re at, or in other (pretentious) words the maturity of your interest in fashion.
If you?re still finding your style I would say the best way to do it is to:
ˇ Go to many fashion forums, that way you?ll be exposed to different groupthink. Try reading fashion magazines, watch movies, people-watch and generally seek various sources of info in a not-so discriminating way. If you don?t know exactly what you need it makes sense to say you?re not set on where it is. Sadly, a negative externality of this approach is that might include sending some money to Condé Nast unless you can find ways to steal their overpriced mags.
ˇ Go to loads of different stores and try garments on, getting a feel of what?s available, once again without discriminating too much. Try to get feedback from other people, unless you plan to live on a deserted island you?ll have to deal with the all-seeing eye of the multitude.
ˇ Get inexpensive items in various styles that interest you and experiment with different looks. H&M, Uniqlo, discount shopping, thrifting and ebay are your friends, and might remain so anyway.
ˇ Avoid deciding what your style is without having worn that stuff for a while?
Let?s say you?ve got a better concept of what kind of fashion animal you are and which messages you want to convey through your garments, it might be the right time to assess your needs.
Remember that unless you literally don?t have the required clothes for a particular activity (i.e. you need to tie patterned silkworm larvae cocoons around your neck -AKA a tie- to denote your station in life and you don?t have any) you don?t actually need an item and especially not fashion/expensive designer items. In other words you don?t have real needs you?re just an aesthete who want express himself through garments or, more likely, a bourgeois who want to show he?s got some bling (hopefully the former).
So what should you get? You should determine what your style is and what it says about yourself then look for key pieces that will help anchor that idealized identity to your persona. Let?s say you?re a rugged American worker from days past with a hint of cowboy showing through. You?re hard working, reliable, humble, physical, manly, etc. A superlative pair of indigo dyed Japanese repros worn pretty much everyday suddenly sounds attractive, even though 2 years ago, when you were an urban bourgeois intellectual socialite those very same jeans wouldn?t have clicked at all.
Once you know what you want to project, brands start coming in handy; these are basically filters that will help you navigate the almost unlimited amount of information and offerings of the fashion world, They?re like those tags you see in some threads. Tom Ford?s Gucci would have, as an example, ?sexy? ?glamour? ?nightlife? ?luxury? ?velvet? ?flashy? ?celebrity? etc. associated to it and our aforementioned worker cowboy probably wouldn?t give it much attention, instead concentrating on, let?s say, Sugarcane ?workwear? ?traditional? ?quality? ?American? ?levi? ?tough? tags. He might also look for some info on brands he?s not aware of but that have related tagging. Now that doesn?t mean he could not come across a Gucci shirt that would be a great addition to his wardrobe, just that, the odds being unlikely, he shouldn?t put too much energy into Gucci. The return on time/energy investment is pretty low considering his criteria, especially when there?s Engineered Garment around.
At some point in his fashion evolution the workwear guy might also decide that his view on the fashion world and relative brand positioning in this world are now an important factor and just say fuck Gucci, as a matter of principle (see Faust?s post). I?ll avoid discussing that view but let?s just say this ties in to both lifestyle brands and market realities (fashion realpolitik, so to speak); if I don?t like the lifestyle Gucci puts forward and even think they have a negative impact on the market I won?t send my money their way, which means I won?t even consider their items.
I know I didn?t get into details and you might be aware of pretty much everything I?ve just said but I guess it?s good to state it again and think about what it means, once in a while.
Note 1: I see little details that the wearer is the only one to know (like natural indigo dyed jeans) as similar to the actor?s trick where they invent a secret about the character they?re playing that they won?t tell to anyone. This little details helps makes the role their own. Of course in that case the role you?re playing is yourself, don?t try to be someone else but don?t settle for a boring version of you either. Remember, you want to drape yourself in signifier that will help you express who you really are, if there is such a thing.
Note 2: Don?t be afraid to break all the rules you?ve imposed on yourself, from time to time, or your style will grow to be monolithic and caricatural
Note 3: Don?t take this stuff too seriously though, it?s only clothes