I tend to move around alot as a GM (and as a player).
When I do get up off my fat ass and start acting things out, I can sense my players engagement rise. I don't just tell them how the vicious but slow fire zombies are shambling to attack; I shamble on over and show them. If the PCs are being interviewed by a bored official, I stand in front of the players, slouching, and read off a series of form questions in a nasally, annoyed voice. I might even record their responses on my clipboard. Getting up and showing rather than telling is a simple thing to do (and seems pretty obvious) but it's rarely used.
I get why; it can be a pretty awkward thing to do at first. Being a bear or a troll or a debutant can feel a little silly just using words. Acting like a monster or wealthy teenage girl can feel downright embarrassing.
Pick your battles. Choose the NPCs and situations that you feel you know the best and get out of your seat, move around a bit. Before long it'll feel like the most natural thing in the world. Your players will dial right in as soon as you stand up, and I bet you'll feel more engaged as well.
As always, YMMV.
(In the last two sessions that a good friend of mine ran, I noticed the difference getting up and about can make even as a player. In the first session I got up and moved around pantomiming what my character was doing. The next session, not so much. There was a palpable difference in how much more I enjoyed the first session with all things else being essentially equal.)
Whatever it may be, big fight or a social encounter, physical movement can punch up a scene. Don't forget that hopping around can net the GM more fun, too. Plus, it's better for your back anyway.