[camlorn]

Unfortunately, I don't have a link, but:

Have a look at the epitaph mud development blogs. He talks about a lot of these issues and his solutions; I especially liked the one on exploration, wherein he talks about how you might have sort-of scripted event nodes with some degree of randomness: i.e. go explore the hill, keep following the road, or if you're skilled enough, notice the grove of trees. Good stuff there, and you should be able to find it through google. That, and his stuff on all the integration with wordpress and phpbb he's doing, but those don't apply here.

Personally:

Never, ever, use the word you in a room description, never ever tell me what I'm doing, and make sure all descriptions work even if I'm coming from the other side; spellcheck and grammar check are your friends; and make sure the room title is descriptive but concise, as many use the brief setting. Avoid the ellipsis, show don't tell, and remember that rooms aren't movies, they're still pictures. If you describe a body falling to the floor because of an assassin (yes, I've seen things like this), remember that body will still be falling when I come back 6 hours or 6 weeks later; if there's a corpse on the floor, make it an item that can be moved/destroyed, etc. The list of things like this go on, but the important thing here is that room descriptions (unless you're doing dynamic stuff) are constant, unchanging, and will be the same forever.

As for world size: not too big. I don't know how to put it better than that, but I've seen a lot of muds where the worldmap is bigger than all areas put together and there's no easy way to find areas, and it just doesn't work. I'm not so much talking about size here as the feeling of size, if you know what I mean: focus on quality, not quantity; if everything is of good quality, move on. Eventually, the world will grow without feeling like filler.

I'm visually impaired, so this particular advice may or may not be useful; I at least agree with it: avoid ascii art, or provide a way to turn it off. If you make an ascii worldmap, provide a clever mechanism for making cool room descriptions from the data, describing the mountain range to the north and the smoke from the settlement to the north-northwest, etc. People always look at this one, when I bring up that blind people can't use the worldmap, and think it has to be a separate system for the blind, but I don't think that's the case. If you go with a worldmap, there's a whole lot of room for creativity with dynamic descriptions and the like.

Depending on specific setting, there's a lot of room for alternative ways of travel. You can provide the 50-room-long road, the magical portal, the train, the interspacial quantum uncertainty device, or maybe all of them. Or maybe you've got a really wierd setting, and people travel about by praying to the great old ones, between islands in the sea of chaos, and your level determines how far you can go/likeliness to survive that particular ritual...

The last thing. A lot of muds fall into the trap of "let's guess the syntax" games. This isn't fun. Really. I've seen a lot of clever solutions to this; consider coming up with one.