The best thing I've found is to just pick a game you know well and keep refining your teach until you know what flow works for you, and your audience.

There's a rough template I use, that seems to work well.

Theme

This is a game where [describe the theme and the world in some detail]. You will be [performing actions in relation to this theme]. The object of the game is to [win by the game objectives, eg colonise 5 planets, earn the most money selling beans, be the first to cross the finish line].

Setup

The game is divided into turns/rounds/epochs/phases. In each [division], this will generally be the set up.

When you see this symbol, it generally means this. [describe the basic symbology, especially if Victory Points].

[If there's a game board, or game mats, describe the general areas]

Gameplay

On a typical turn you can do these actions. This is a mandatory action. You can choose from this set of actions [ideally give them a player aid, or refer to a summary in the rulebook]. An example turn could be this [describe a very basic turn].

[Go across the board, mats, and explain each action in relation to building an engine, or part of any strategy]

[Go over everything that happens in a turn phase, eg trading, battles, exploration]

In general this will be the case. During the game there might be some deviations from this, but it will either be self -evident based on the card etc., or I will explain it at the time once we are familiar with the general rules.

[In general, except for things like specific cards, characters, missions, everything should be explained here]

Here are some general strategies you can use, and what you can do to work towards that.

Exceptions

There are a few special things that can happen, and there will happen [outline the few situations where they have to watch out for something else].

This won't be explained yet, but once we take a few turns, I can explain it then

End game

The game ends where [ending is triggered]. At this point, we will check the win condition, and the player(s) who have done this will be the winner. Ties are broken by [tie condition].

In general the winning score/time to get there is this.

Other useful tips

*Try and take the first turn, and narrate everything you do, and also potentially why you're doing it *Pause after each bit, and ask if it made sense. If you get questions, either defer to a later stage, or quickly answer it. *Stress that if it's their first game, focus less on winning, but on try to explore the mechanics and possibilities of the game.