In order of importance, a decent grinder and a scale should be at the forefront, along with using some quality beans!

The next up would be any brewing method, and this can be tough to navigate. If you are lazy, go with a normal electric filter brewer. If you mainly brew 1 cup at a time - Aeropress, cheap - quick - effective and easy to use Steep coffee - french press (I'm not particular fond of this myself, but flavour is subjective) Pour over - I'd probably reccomend a v60 here, but would require a kettle or something that lets you control your waterpour as well.

But you can do it in steps! If you consume a lot of coffee, you could start with a brewing method and a scale, then get your beans ground in a coffeeshop as you buy it. Not ideal, as freshly ground coffee is a huge upgrade from pre-ground, but it gets you to experimenting faster