Trying not to be too repetitive in what’s already been said, so here’s a little exercise that I like to do, especially for when you get to making your own maps.
Pick out your favorite FE maps you’ve played. They can all be from different games, it doesn’t matter. Just so long as they’re the maps which felt the ‘best’ to you, whether it’s due to its layout/flow, enemy compositions, story integration, feeling difficult in a rewarding way, whatever. Then, look for commonalities between each of the maps.
They’ll probably follow most of the tenants other users have already outlined, but as someone who prefers to see things in front of me > theory, I find it’s a nice way to hammer those points home.
Also, it’s just generally nice to have a short list of inspirations! If you’re about to burn out while troubleshooting your own map, remembering why you’re doing it in the first place is always a nice kick in the rear.
You can also do this in reverse with maps you like the least, and contrast them with better maps with a similar structure and/or objective. Maybe you lost a unit under circumstances which felt unfair, or you were stuck spamming ‘Wait’ on an iffy ‘Defend’ or ‘Survive’ map. Then, brainstorm some ways you’d fix those problems for fun.
One last thing,
Something I’m personally a fan of is when FE’s maps and story feel like they were clearly written alongside each other, as opposed to feeling like we wrote the script, then went through going, [map here], [map here], [map here].
I would prioritize the more technical aspects the others outlined first, if you had to pick only one, but still: A big part of making a map memorable is being able to clearly place it within its context in the plot, too. There’s a reason the most beloved maps tend to be ‘setpiece’ maps, for lack of a better word, versus filler bandit skirmishes.
That’s not to say bandit skirmishes don’t have their place, of course. Not every map can, or probably should be, a showstopper. Both for the sake of not burning out the player and for plot cohesion, I think maps are at their best when their difficulty ebbs and flows in step with the script’s plot curve (Roughly. If the ptag just suffered a major loss, that’s probably not “easy chapter” time, it’s probably “break the player’s kneecaps” time, haha. Hopefully that makes any sense, idk).
Done well, you can order the maps like a storyboard, since the maps are so inextricably linked to the plot. Done poorly, the maps might look like open field/forest #10002 and be hard to parse from one another at a glance. I think I saw you mentioned vanilla FE earlier, so this example might not be the most useful to you, but 3H is my go-to example of the “open field #10002” issue, especially early-game. Without even getting into the maps feeling samey on a mechanical + layout level, playing multiple of these maps in a row feels like you’re spinning your wheels, as opposed to traveling and progressing, which is the feeling that FE generally excels at. It doesn’t really feel great on a player level. I believe that game’s maps are fairly well-documented online, if you want to check some examples out.
Best wishes for if/whenever you make a hack! I’ve started plonking away at one as of a couple months ago, and it’s quite fun.