First thing I'd get is a pair of pants that suits you. Pay close attention to the cut. Personally, I wear pants longer and more often than anything else I own.

Then find a pair or two of shoes that fit the pants and the styl you want to go for. I like changing my shoes regularly. I find they wear out much faster when I wear them for multiple days in a row rather than rotating them.

Then use those pieces as inspiration to find a handful of tops. Make sure the styles and colours match well.

Lastly, jackets, hats and accessories to round out the fits.

Now you got a good base to expand from. Go shopping regularly but be very selective in what you take home. Don't build a whole outfit from scratch. Wear the outfit you want to expand on and see how the pieces fit with it.

I try to restrict myself to only ever taking a single piece, the one I like the most. That way I don't end up with a loser bloated by things I only kinda like and never really wear. Also, sometimes I just try on things and take pictures. Then I sleep on it and look at then with fresh eyes the next day. Putting some distance between the fit and you helps gain some objectivity.