I don't really have enough time to make a full out tutorial, and I'm not aware of many myself. Sorry - most of what I know is intuitive. My best advice is that you do plenty of mapping, look at plenty of other maps, and pay close attention to what looks good. Chances are, if it looks off, it probably is.
Well you see, the thing with XSE is that the #dynamic command makes it so that XSE automatically searches for free space.
If you tell XSE to start at the end of the normal ROM space, it will automatically place scripts there, and the after a while, into the expanded ROM areas.
So, I suppose #dynamic 0xF00000 would suffice.
That will make XSE place scripts at 0xF00000 and later, saving the space from 0x800000 to 0xEFFFFF for maps, graphics, or whatever... though I doubt you'll actually NEED to expand unless you've done some HEAVY modding, I'm talking about a hack the size of Rijon Adventures, which happens to be so large it requires the ROM to be expanded.