I have often found that the audience at a demonstration gets the most fascinated with the soft and silent mae ukemi falling. That amazes them, sometimes to the extent that they hardly notice the rest of the demo.
It is important to decide why you do the demo. If it is to get new beginners, don't scare them off by doing too many very dramatic techniques. If the spectators are very impressed, that usually means they think that they could never learn it.
Also, don't be too serious about it all.
I try to show the audience that we have fun training aikido.
Another thing: people in the audience don't see much difference between pinning techniques, or one technique done against different attack forms, or different jo kata, or partner sword exercises.
Try to make a variation that even those with no knowledge of aikido can perceive - such as suwariwaza, several attackers, different weapons, defense against them, and so on.
Think of the whole demo as a story line, preferably building up to a crescendo, but at least changing significantly from the beginning to the end.
And don't try to show it all. People will just be confused if they see too much.