Fun world values: add a 0 to megabeast/titan/vampire/werebeast/demon counts, don't put too many layers between uh, 3 and 4 I think, while it does give big freaky tall candy spires when you do, it takes forever to get down to hell and such like that, and as big a fan of vertical forts as I am, going down through a 150+ z level world-gen ramp spiral as an adventurer is a nightmare.
Put elevation variation up and you get an interesting mix of landforms which let you have fun neighbors adjacent to each other, don't set cavern openness too low and passage density too high, it's just annoying and cluttered looking, unless you like densely packed cavern tunnels I suppose?
Some people like big huge worlds, but in fort mode it means enemies will have to travel forever to reach you, even on a 65x65 world it took four years for my first real siege, though part of that could be due to the goblin civs in the central area of the map being at war with each other, so only the far northeast civ attacked me normally.
A 65x65 is big enough for a surprising amount of variety, history, and civs can spread out enough to get established and then start really grinding each other into paste happily, plus it's a good size for adventuring on, you can travel across the map in a reasonable amount of time if you really try, or you can spend literal years in-game exploring everything. Turn all the rejection values at the end of the advanced settings off or you might miss some interesting results. Play with the good/evil square values some if you're after a certain mix, but even with the default values in a 65x65 you will end up with occasional maps that are packed with evil or with an island of good biomes and wilderness/evil all around them.
Don't set good too low or you won't get dorfs readily, don't set max elevation too low for the same reason, I like elevation variation 3200x3200 because it gives chunks of mountains instead of big bands or half the map being blocked off and dead. Toss in a few mountain peaks for the fun of discovering them, a similar number for volcano minimum for the fun therein, go for a north or south pole rather than both so you can have a desert at one end and ice at the other, and if you want it on a desert sea try to set it to one or two partial edge oceans to give a better chance of finding the sort of site you're after.