In calling to a mixed group, which you're pretty much always doing, you have some people who know how to do a figure and others who don't. One approach is to describe everything in terms of basic movements:

Ladies take right hands, pull by, and stop facing out with your neighbor on your left. Gents, take your neighbor's left hand in your left hand. Ladies, put your right hand in the small of your back, gents put your right hand on it. Ladies walk forwards, gents back up, until you're both facing into the set again. This is a "ladies chain".

In the case of ladies chain this is rarely the right approach. Most of the dancers already know the figure, and most of those that don't will learn it better from the others than from your verbal description. If you simply say "ladies chain" and leave some time for dancers to show it to each other, it usually works.

But what about figures like "mad robin" where fewer dancers know the figure and it's harder for them to teach each other because it's disconnected? Most of the time I'll teach it reduced:

Dosido your neighbor. (pause) Dosido your neighbor while looking at your partner. (pause) This is a "mad robin".

(After teaching something I want the dancers always know what it's called so I can just say "mad robin" when calling the dance.)

If more people know it I'll first tell the dancers I'm about to teach a mad robin, then teach it:

In a minute we're going to do a mad robin. But first dosido your neighbor. (pause) Dosido your neighbor while looking at your partner. (pause) This is a "mad robin".

If even more people know "mad robin" I'll leave off the initial neighbor dosido:

Don't do it yet, but the next move is a mad robin. Dosido your neighbor while looking at your partner.

When you "pre-announce" a figure, however, you need to be careful. During a walkthrough many dancers will start a figure as soon as they think they know what it is. This is usually a good thing, because it shows other dancers how it starts and keeps the walkthrough short, but if you want to grab a spot for teaching between identifying the next figure and having them walk it through you need to be clear about it. I like:

Don't do it yet, but the next move is a mad robin.
The next move is a mad robin, but wait!
In a minute we're going to do a mad robin. It ...

They all communicate to experienced dancers that they shouldn't start the move immediately.

(I don't regularly call any dances with mad robin in them, though, partly because I want to stick to core figures unless I'm calling to a crowd that's quite experienced and is going to get a kick out of doing less common ones.)