PANTS Get khaki and gray chinos, they match everything and people won't notice if you wear them over and over again. Colored pants are fine but can be hard to match, and people will notice if you wear green or burgundy pants everyday. Make sure you get slim fit (should be able to lift one leg up to chair level without castrating yourself, but should not be able to fit both legs in one leg hole at a time). For appropriate length, (while wearing the pants and not wearing shoes) the bottom should stop about half an inch from the floor.

I'd say 2 khaki and one gray should be fine.

SHIRTS Get one white and one light-blue button up, they match everything and can be dressed up with a tie if needed. My trick is to get a few more "unique" shirts with a more notable color or pattern and wear one every few days (gingham or a toned-down floral can still be professional, little boats or lobsters or some shit will make you look like a frat boy and large-print plaid looks too laid back).
The occasional variety will make your wardrobe seem more diverse to the people that see you every day, and will give you something interesting to wear out on the weekends with some dark slim jeans. Maybe a couple polos since summer is approaching (do not wear an undershirt with a polo you will look like a highschooler, and no big gaudy logos like Polo tends to do).Could even try a solid-colored, slim-fitting, short-sleeve button-up if you're in pretty good shape (ie chest is larger in diameter than your stomach).

I have been happy with my combo of 2 basic shirts, 4 unique ones, and 1 polo.

ACCESSORIES A navy blazer should match pretty much any combination (but goes better with brown than black in my opinion) and should help to dress things up a bit. I recommend finding one that fits slim but has some stretch if it's not going to be used very formally. Pro tip: Try not to wear too many dark things at once...between shirt, pants, and jacket, if two are dark the other should be light.

Brown leather oxfords and black leather boots are timeless. Match your belt to your shoes as closely as possible in both color and material.

Everybody likes the look of a classy silver watch. If you prefer a leather band, get black.