Focus on the basics and the things that you're good at and enjoy; things you have strong confidence in. This way, you can explain the details.

Recognise the level your teaching, that's the best advise I was given. No point teaching the crazy brown belt shit you no doubt know if your mat is 80% white belts.

Pick a subject and stick at it for a month. This helps it sink in, learning something new everyday may seem cool at first but it's unlikely that it will be retained to any level of proficiency. I recap the previous lesson as part of the warm up with one of two reps each.

Try and keep it fun, remember people do this to escape the everday shit. If you or them aren't enjoying it, what's the point?

Firm and fair.
Your students are a reflection of you! If you see something on the mats that makes you raise an eyebrow or think "would I like that if I where in that position". Nip it in the bud.

Set expectations and keep to them. You want people to be 10-15 minutes early, be there 20-30 minutes early. You want people to bow and shake hands, make a point of doing it at every training. Consistency is EVERYTHING!

That's what I do but I'm keen to hear anything others are willing to add, could improve my teaching as well.

Good advices here.
One more... Plan your classes in advance.
Build and structure your classes.
What games/warm up drills?
Which techniques? In what order? How much time for each part? What questions could arise for each technique?
Write it all down. Structure it well. Save it for future use. I keep my class plannings since 2015. You can always go back to a class you did 2 years ago with the techniques, details and structure you did before and redo it.
A good and structured class, prepared in advance, can make all the difference!

Good luck!

That's brilliant!
Something I forgot to say. I too keep a diary but I don't put as much detail into it as mentioned. I will definitely be doing this from now on.

Watch a bunch of instructionals from different instructors with an eye to 'how' they teach rather than what they're teaching. I really enjoy Chris Paines, Charles Harriot and Priit. I take some ideas for how I teach from how they teach. You need to have your own style but take what works from others.

1. Have a plan. I've got a spreadsheet, listing everything I'm planning to teach over the next few months. I'll watch a load of videos to see how other instructors have taught the same technique, plus I generally teach the same thing over and over again (spacing it out a lot, so at least 6 months between classes when it's the same thing).

2. Talk slower. No really, slower than that: you're talking faster than you think.

3. Less detail. New teachers tend to get excited and show EVERYTHING. Students are neither going to remember it all, or have the attention span. You can always add extra detail when you're wandering around as they drill.

4. Get feedback. The people best placed to tell you how to improve your teaching are you students, as they are ones who are paying you to teach. Obviously you don't have to act on every bit of feedback, but it's really really useful to know what students actually want from class. I did a bunch of surveys when I first started teaching (particularly the women's class), very handy.

5. Make sure you do multiple angles, ideally also wear a different colour gi than your partner. Always ask if people want to see it again.

I'll say from a student, Kid's coach, and fill in emergency adult's coach I think having a pre plan is very important. Know what you are doing for the next month or more so you can be fully prepared to teach class every day. I really enjoy as a student when we really dive in to a specific position for long periods of time. For example, spend a month on only Mount working top, bottom, attacks, escapes, theories, submission chains, etc. So every class you come in will continue to build your knowledge, skills and abilities in one specific area. I also prefer that warm ups be Jiu Jitsu specific drills vs just random calisthenics. I think each class should have time for drilling, positional sparring and free sparring.

^This

How often and whom would you actually teach? It's very different for having your own "group" vs substituting in 1-2 classes per month.

What about the ratio of Gi and no-gi?

Accept that students only remember 20 per cent of what you teach max

Have zero expectations, be patient and always bring positive energy.
Never lose your cool or get frustrated when someone doesn't get it.
Don't over explain. First teach the gross motor movements.
Add details only after they can do the basic movements.
Accept that your teaching style won't appeal to everyone.

https://youtu.be/hvLED0fJOQM
I like this video, Brent explains that transitioning from Gi to No-Gi is easier than the other way around.
I tend to agree.
That doesn't help you much as far as ratio goes but I will usually do No-Gi the whole of summer, it gets warm in NZ.
Then I'll drop in a week every couple of months excluding winter, it also gets cold in NZ. But that's purely because I train in a shed with no insulation and no way of heating or cooling it.
Nothing wrong with 50/50 though that what Marcelo Garcia does and his students and him are beasts!
I would tend to lean towards Gi though because I like choking people with their collar. Teach what you enjoy that's how your students will get the best from you, at the end of the day that's what it's about, the students. Like I said in my first post : "if you or them aren't enjoying it, what's the point?"

IMO, that depends entirely on how much you like both. I absolutely HATE nogi and avoid it as much as possible. I therefore have somebody else teach the nogi classes at my gym. If you're the only teacher at the gym, then teach it if you like nogi. Controversial opinion perhaps, but I don't think it is essential to have nogi classes at a school.

If loads of your students are desperately clamouring for nogi and there is nobody else who can teach it, then I guess in that situation it would make sense to teach nogi. Fortunately for me, I'm not in that position. That would be a worst case teaching scenario for me. Even worse if I had to teach the kids class, I find children very annoying. :P

Be yourself and have fun with it.. If you have fun it will help them enjoy it... Remember everyone learns differently so encourage them as much as possible and don't get frustrated out job as instructors is to help each student learn at their own pace.

Stay positive and ask for criticism. As said above watch instructionals with an idea for looking toward methodologies you are comfortable with and feel natural to you...

Be patient with yourself and remember just like BJJ itself teaching is a learned skill and you get better as you do it..