Writing a description
A description can be set using the describe command. A good character description gives people who look at you a vague idea of what you look like. That's it. Of course, you can put other stuff in there, but should you? No. Here's why.
Write for your audience
The too long didn't read principle might seem counter-intuitive to apply in a MUD environment, which is constructed from text after all. But enjoyment of a MUD does not necessarily require that all output that is sent to players be read, and once familiar with MUD mechanics, players will make their own choices about which output needs to be read and how closely.
Many people play with brief look turned on and many who use verbose look recognise rooms by the shape of the text or an ascii map output, not by what the long description actually says. When a player is standing in the same room as you, they might look at you, but if your description is too long there is a fair chance they will skim through it, or skip over it.
If your description is worth writing then presumably you want people to read it, and they simply won't do that if it's too much effort. However, anything over three lines could well represent too large a block of text for a player to want to spend the time to read. As a rule of thumb, under 240 characters is recommended for player long descriptions, or the equivalent of three lines of text when using an 80 column window (a setting used by many people).
Keep in mind when writing your description that you don't know who's reading it. It makes sense to have "You feel quite intimidated by him." in your description if your audience is weaker than you, but what about when you go to learn from Lanfear? Is she really going to be frightened of some level 200 assassin? The same goes for things like "She is the most beautiful woman you've ever seen." How do you know? And what about when two people have that in their descriptions? Do they keep getting more attractive as you look back and forward between them?
Describe your character objectively and without reference to the viewer. You're not in control of their character and it's rude (and often wildly inaccurate) to presume you know what their reaction will be.
Are you a robot?
Do you smile every time anyone looks at you? Of course you don't. Sometimes you don't like them, sometimes you don't notice, sometimes you're in a bad mood, whatever. So why would your character do it?
Lines like "He sees you looking at him and winks." are a common mistake. If you want to wink at everyone who looks at you, you can do that. Just wait till you see "<Player> looks at you." and then respond. Not only does it allow you to modify the action based on context, but it cuts down the length of your description, making people more likely to read it.
The final thing you should do is check your description for spelling errors, typos, grammatical errors, etc. Of course, you should do this for any writing you intend others to read, but it's worth mentioning as it's so often overlooked.