One big difference between roleplaying on an MMORPG and in a lot of other mediums is that there’s a visual representation of what the world around you looks like. Of course, in other mediums you have descriptions and all kinds of other things, but having an actual image of what it is that your characters are looking at can be a lot of help in roleplaying.
One of the main ways that this is done is just by being aware of what’s going on around you – for example, if you’re roleplaying having a toddler walking around at your feet, it’s probably best if you move away from the staircase first. If it’s snowing outside and you come across a campfire, why not sit down right near it and make reference to the warmth, rather than just picking a spot wherever? Heck – when it comes to places to sit, why not position yourself on the table instead of on a chair? I’ve seen many variations on this theme, ranging from climbing statues to sit on the top, to climbing furniture to perch on top of the bookshelf, and if done with some kind of in-character justification (ranging from ‘I’m more comfortable sitting here’ to ‘This is furthest from the rotting man in the corner’) can really be an asset to a scene if done properly.
It doesn’t even have to be as serious as this. I have a character who is exceedingly nervous of coming into physical contact with other people, and whenever anyone stands too near her (really, why would you want to be standing on top of each other?), I make a point of making her back off a few paces. This is particularly effective when the other person notices and continues to back her into a corner because of the difference in their personal space bubbles.
Actually noticing these things can be difficult, of course. If I so much as took my eyes off the screen for a second to talk to someone in real life, I’d miss something subtle like one person taking a few steps back from another. If you want to do something like this and make sure everyone else notices, you can always back it up with an emote; in the example I gave above, following up the backing off a few steps with something like ‘/e shuffles back a few steps awkwardly’ could get the point across if they happened to miss your first move. Still, make sure you do make that first move – if you emote moving back and stay standing on top of one another, that could just get awkward.
This applies to things like taking damage. If you accidentally step in a fire and take damage, stamp around and yell, “Ouch!”. After a battle, reference the fact that you’re not doing at all well and that you need a moment to bandage your injuries. After all, even though you know your character will recover if they stand still long enough, it still hurts to be knocked down to half their original hit points. Surely they’ll be experiencing at least a little bit of pain and suffering after an intense battle.
Making use of the environment around you, and making use of the fact that you can see how each character is moving, generally, can really improve a scene.