I won't be a big help since I was lucky enough to learn perspective at school when I was a kid (which is pretty rare as far as I know, but I had a great art teacher : Mrs Gaucher, if you're around : thank you so much !!), so I don't have many references to share.
In my opinion it's a good idea to start with isometric to train your hand and your mind, if I can say. For isometric, you can easily find or draw a simple grid and start building your shapes. It mostly needs logic and a little practice. Start with simple shapes : cubes, parallelepipeds, then add a roof, try L-shapes, etc.
In a second time, you can also add a first vanishing point to isometric and create something more complex (a good example here) : it's a good training before traditional perspective, and you can already create super cool icons for your maps with that.
Traditional perspective is harder, but here again, it's mostly logic. You can obviously find tons of great and simple explanatory videos for first concepts. Most of them will teach you 1, 2 and then 3 perspectives points, perspective lines, vanishing points, horizon, elevation... The basic concepts are simple, but harder to put into practice, so here again, don't start with complex buildings and just practice with basics : start with a simple cube in different elevation and rotations and just 1 vanishing point, then 2 points, then 3, until you masterize the first concepts and are ready to go for something more elaborate. I had a quick look on Youtube and found this one with a cool step by step : here. It's all what you need to start
General tips :
Once again, start simple (cubes, tons of cubes).
Take a step back, it's easier to spot errors ; things have to be consistent and your eye is already accustomed to perspective. Visualise. Be logical.
Walk outside : a street is the best teacher for perspective : look at how lines converge.
For me it's easier to start on paper with a ruler, but try both digital and paper : you'll see the feeling is different, and you won't see perspective with the same point of view. Rules are the same of course, but find the way that will make things easier and more comfortable for you, so you can just focus on perspective without any other concern.
And... good luck ! You're right : that will be a whole new world, and I know you'll make great things here !