The advice that I wish I got when I started with botany is to start out by learning the families, all of the families you may encounter and have a really rough idea where they fit into the tree of plant life. It sounds a little insane, but start going through the families on Go Botany and get to know them. For smaller families with one or two members its as simple as looking at pictures and recognizing “this weird looking flower is in Acoraceae” or “Sundews are Droseraceae”. For bigger families you’ll have to read a bit and probably go to sources outside the flora to find synapomorphies of the family (look up that word if you don’t know it). This for me becomes a fun thing because you see all of these wild plant forms, and realize that your conception of a grass, or dicot, or fern is wildly narrow and fails to account for some of the crazy diversity even in your local area. Now you won’t actually remember every family, but when they come up in keys or you’re stuck you will have solid foundations for where to go and what that means. It will feel like a lot of work for minimal reward but seriously puts in a ton of ground work for the future. If you find yourself in the general key of a flora often you’re not using it right (this is not a thing that is valuable for most users most of the time).
Once you have your families good enough that you recognize a decent portion of what you see to family go out and start keying. Key some hard groups but key some give-mes too. Don’t key (at first) if you can’t find everything the key talks about. Don’t skip the key because you think you know it, and use CV as an aid in checking how you did not a first pass. Keying is where I learned most of my species, and always had a good idea of what I was and wasn’t seeing. You quickly learn what you have and can pick them up without keys soon. Keys also help you focus on what is different in a genus which varies genus to genus. Once you recognize species by what distinguishes them you realize that a lot of the species pairs aren’t so intimidating (like native Phragmites which looks nothing like the invasive :) )
This method lets you get to a useful place in the flora without a general key, and gets you actually learning the differences between species. Pretty soon you get to know most of the plants you see. Even now I find myself checking keys to make sure I’m not falling into bad habits and traps. That method means the things I learn are families and specific species I know (and eventually you know enough species that you get to know a genus)