In no particular order:

1. Call for the dancers that are doing OK, not the ones going wrong - they can put your timing right off! You can alway stop the dance after a few times though for a bit of extra instruction if necessary.

2. Figure out two different ways of describing a tricky figure during the walk-through, one geography-oriented, the other person-oriented (e.g. the one on your right diagonal versus 1st man and 2nd lady). Some people think better in terms of one rather than the other.

3. Have an assistant / spouse / partner, with sharp hearing, on the dance floor. Get them to feed back any comments overheard from the dancers, moderated if necessary.

4. Really know your dance. Caller Bob Archer recommends being able to dance it mentally in every position simultaneously while you call.

5. Learn from other callers, including those that are less than perfect. Seize on directions that were unclear, for example, work out why, and come up with your own version to avoid the problem.

Oh, and most importantly,

0.   Enjoy yourself!