It's highly unlikely you will just happen to find upgrades as you get farther into the game. You're going to have to buy or craft most of the items you will use once you have completed the campaign. As others have said, the first step is figuring out what you need.
For example, capping your elemental resists (75% Fire/Cold/Lightning resistance) should be your first priority, defensively speaking. You'll want to prioritize gear that allows you to cap your resists efficiently, so that you can squeeze other stats out of it. For example, a ring that has two resists at 40% each is likely much better than a ring that gives you three resists at 20% each. Anyway, it's up to you to find out how to cap your resists while also getting enough damage and utility out of your gear.
As for uniques, they tend to fall into one of four categories: crap (most of them), leveling uniques, build-enabling uniques, endgame uniques (the ones you see people using in busted builds or selling for a ton of currency). Depending on what you are playing, you might use none or a few uniques. If you post your poe.ninja character link, people can take a look and let you know what you might consider trying to replace/upgrade first.
Here's mine: https://poe.ninja/poe2/profile/Auturgist-8134/character/Kellistara
Anyway, once you have your resistances capped and you've got any build-enabling uniques you need, you shouldn't have any trouble making noticeable progress. If you want to DM me any questions, I'd be happy to help you further. I can maybe even throw you a couple divs to buy some gear if you need it, too.