A good pair or two of dark jeans. A cheap entry point would be Levis- 511s are a good, somewhat skinny fit. 514s are the best for weight lifters and slightly heavier people. 510s are skinnier than 511s, and ideal for the super-thin. Levis is not a perfect brand, but a place to start, and incredibly affordable for most.
Oxfords, black or brown. Plain toe, cap toe, or wingtip. No square toes period. The slimmer the better. Preferrably black, but thrown works as well.
A few button-down shirts. At least one white. As slim as they can fit without looking overly stretched. These can be paired with anything.
A pair or two of slim trousers. Pinstriped, windowpane, or anything you like, so long as it is relatively conservative, goes with th above shirts, and fits well.
Good socks, underwear, and T-shirts. Get nice black socks. Do not wear white socks with your oxfords, ever. Boxer-briefs are the best choice, underwear-wise. Get a few good v-neck t-shirts that fir you well, but do not wear them excessively. Also, if you have a sweat issue, purchase good undershirts.
A good wool coat. Leather is okay, but usually too pricey. Peacoats, though slightly played out, are an option.
A good suit. Two button, slim cut, preferrably in a dark gray or black. The slimmer and more fitting, the better. Brand is largely irrelevant (at this point) so long as it fits well.
A slim Tie. In black or another conservative color. No odd patterns, If you're massive, stick with a normal sized tie.
A leather belt. Preferrably reversible, always wear it with your jeans or pants, never with the suit.
Weather-appropriate clothing. Sweaters (including cardigans), rain coats, gloves, etc. Whatever you need to function correctly in the weather.
Low-key accessories. A scarf or two. A nice, bifold, slim leather wallet. A pocket square.
Everything must be tailored. Fit is everything. You can have the most expensive, coolest clothing in the world and still look like a tool. NO matter what- no matter the price, the article, the style, whatever- get it tailored, buy it to fit, or do not wear it.
As a caveat to the above, Dress to your size, not to what others tell you.
Super skinny pants look good on super skinny people only. This does not make them more fashionable than you can be. Those who obsess over being a thin as an attempt to be fashionable are misguied and insecure.
Nothing "Graphic", Ever.
No graphic tees, no graphic designs on your pants, nothing. Ever.
Dress like a proper human being.
Do not derive fashion ideas from movies, video games, music or any other form of media. No matter how much you may like whatever it is you like, it likely is not a good idea. Trying to incorporate something you saw in video games, is a really bad idea.
Stick to simple colors and earth tones until you build up to a good wardrobe.
Do not feel scared to dress well.
There is no negative to looking good. People who make fun of you should be ignored, they are trying to accomodate for their own securities.
Create your own style.
Listen to everything anyone says with a grain of salt. Create your own style. Your ability to mimic what you saw on some webpage is not the judge of fashion in the real world.
WHERE TO SHOP
Nowhere is off limits. Shop everywhere. Try everything on. If you buy online, ensure they have a return policy. Never buy from Korean/Chinese Ebay retailers. Vintage shop and check out your local salvation army. No matter where you shop, never expect a perfect fit: Befriend a good tailor.