Kind of depends what your personal style is, but experimenting and trying stuff out might be the only way to discover it.
Here’s some stuff I’d look into:
Jackets: I think seasonal fabrics are a good way to go — but pay real close attention to the details and decide what you want (or what you want a tailor to add). For the colder seasons, I was really into tweeds last year. You could easily have suede patches added or look for options with a throat latch. And, given tweed’s almost infinite variety of colors and patterns, you can definitely find either a conservative or wild pattern.
This year, I’ve been sniping cashmere jackets on eBay. Feels great and for some reason it’s not being discussed as much right now (maybe because a lot of readily available brands don’t have 100%-cashmere jackets available?). I’ve got three I need to take to the tailor.
As for spring and summer, jackets in madras, linen and seersucker are worth hunting down right now in eBay. I think summer really encourages more outrageous patterns, especially on the weekend. Again, I’d be picky about details.
Knitwear: I’m pretty stuck on chunky knit shawl-collared cardigans. Derek at dieworkwear really likes shaggy-dog sweaters. I also think that a tennis/cricket sweater is pretty neat. Brooks Brothers has a few right now, but they’re also on eBay and Etsy quite frequently. Find a design and color you really like and buy a great one that’ll work with a majority of your wardrobe as a layering piece. That’s the logic I used behind mine and I have zero plans this year to buy more sweaters.
Shirts: Custom-made shirting. I’ve said this before, but I prefer MTM services where you have a tailor measure you in-person instead of submitting your own measurements (either off a shirt or self-measure). Study up and get nerdy about the details you want.
Other: Neckties. Edit your tie collection and build it into something great with quality pieces. This process will probably take years unless you’re filthy rich. I guess this advice could also be given for every element of your wardrobe.