My first thought is a question.  What is the level of audience you are going to speak to?

For instance, some of my audiences are beginners and we need to do port-starboard.  Others, we can do rules 10-17 and others we can also talk about 18.

a google search will pop up with more pages of links that you'll want.  Two of which could include (not necessary recommended):
https://drive.google.com/drive/folders/19essv_KGDphubDSIWxkS57pi2A9789O- 
http://morainesailingclub.org/website/racing/LEARN%20TO%20RACE.ppt

One suggestion is it present them as you race.  I.e. begin at the start, then windward leg, windward mark, etc.  linking the rules to the leg helps me to apply them better.

The audience is mixed, but mostly at the beginner to club racer level.   Most people are cruisers who do a few "local" races in the season, but some do Spring and Autumn series and know the basics.
I would assume R10 to be pretty basic knowledge, but I'm sure a few wouldn't recognise the windward "running" boat on stbd, to have ROW over the Port boat beating to leeward.   

.... a good tip TJ

Start with a magnetic white board, a black pen and your Healy boats. 

Start your talk about what rules apply prestart, during the start and immediately after. Entertain questions. No more than 3 to 5 if they're short.

Next: Talk about rules that one may encounter on the upwind. Entertain questions. No more than 3 to 5 if they're short.

Then for the fun part, show scenarios at the top mark, with and without offsets. If it is a group that does mainly distance races, go for RRS 18 light. (If you're inside, you're inside. If you're outside, stay outside around the mark.) If they are buoy racers, be prepared to spend some time at the mark. 

Then show what happens at a reach mark. This should be quick.

Do the downwind rules and then the bottom mark. Be sure to explain why some of 18 is different at the bottom and where the language tells us about those differences. This won't be quick.

Then show the finish and immediately after.

Videos and diagrams are nice, but they can be limiting to what you can show when a question is outside of the diagrams you have. Keep it conversational. Show them that we use the book too and read the applicable rules aloud. Better yet, have an assistant that can show the rule in discussion on a screen and have them read the rule so you have more than one voice for the poor souls to listen to.

What I just laid out is about 3 to 4 hours depending on the group. The group will pace themselves depending on their knowledge. The more they know, the more they will challenge you. Be prepared to tell them that you don't know the answer and that you will research it and send out to the group via email. Keep them from rambling and keep the conversation under control so you can keep the group going around the course. Be careful of the person that will have a lot of questions and will hog the presentation for themselves. Ask them to note their questions for afterward. 

Watch the time and change pace as needed to finish close to where you should be at the time bell.
 

I use a simplified version of Coach Pat Healy's presentation on the Keep Clear concept.
Advantages are that it follows the reasoning and orientation of the Rules, and provides an easy way to learn the active rules by number.
(I raced for 40 years "knowing" instances when I had ROW. "Keep Clear" gives a fuller picture.)
Attached are
my handout sheet - easily drawn in progression on a chalkboard/whiteboard.
a powerpoint of Coach Healy's full version (note RRS shows 4BL for radio sailing)
a handout of the powerpoint - which include props to Healy and shows 3BL

the simplified version handout  in pdf

USSailing.org has a power point "A round the race course" about each rule(s) applying at each spot on the race course on its web site - I cannot copy and paste the link here but if you ask U S Sailing they should be able to get it to you. 

I like the idea of focusing the discussion on obligations rather than rights.

Also, if you want something beyond the usual "port-starboard, windward-leeward" recitation, I've often thought that a session on the protest hearing procedure would be useful for racers. I think competitors would do better at preparing or defending against protests if they understood the procedure and what the judges would be looking for. If they write, testify and question with a view towards establishing facts relevant to the rules and suggesting conclusions it makes the hearing more efficient and can enhance the probability of successfully sustaining or defending against a protest.

I have been presenting the RRS for a while and the YouTube video set up by Laser District 8 has proven to be pretty popular.  It can be found at https://www.youtube.com/watch?v=3Sbz0AYZg6k 
It starts with a basic presentation of the fundamentals and then runs around a windward/leeward/windward/finish course beginning in the pre-start using a white board and magnetic boats. Feel free to steal whatever works for you.
Eric

How long is your time slot? I helped create the ILYA #FairSailing presentation. I can send you a copy of the PowerPoint if you want to use it. It is long and detailed, so consider the audience. With questions from a medium size audience, I usually do 2 nights of 1.5 hours each. It usually breaks into the first night being the rules up to buoy room, then the second starting at rule 18. There is advertising in the presentation. You can see a couple of us presenting it here: https://www.youtube.com/playlist?list=PLx-QD0qI_uN-OeIMIHSr5BpWRUoRuLei3&feature=share 

As you are in the UK the local rules advisor will come for no fee and talk to the club on rules. As jacqui at Rya and they will put you in touch with the local rep if you cannot find them on the RYA Web site. It is a great service. 

Mike just beat me to it - Talk to your local Racing Rules advisor - even if they can not do it they will have access to PowerPoint presentations to use as a starting point - saves re-inventing the wheel.

Thanks everyone for your input and attachments /links.   I'll follow them all up as I put my talk together.  
Mike 

I did these diagrams for my pupils.
https://photos.app.goo.gl/BDERmDWuEeJNoviR2

Keep in mind that done properly, you will learn more than you think.