As always, it's my opinion.
1. Don't chew food when you explain things.
It sounds very unpleasant, and shows that you can't behave properly. Same goes for 'gulp-gulp' drinks.
2. Don't wave your d*ck in front of every watcher's face.
I mean bragging. Like when you say that that picture took you half an hour, when it actually took you all night. Or when you say something like 'Colouring? Bah! It's not a problem for me!', and then you torture your photoshop colour wheel for the next 9 hours, trying to 'make it look good'. Your watchers are no idiots, and they understand when you brag, and when your words are not backed by your deeds.
3. Compose a list of 'milestones' before recording a video.
Not every person can produce detailed, yet simple explanations on the fly - that's why you need a 'talk plan'. I know that you could mean well, but it is quite tiresome to hear constant 'Err... Well guys, errr... I mean, line art, yeah, line art... Well... What can I say...'
4. Watchers come to your channel not to spread the word about your 'awesome art', and not to praise your skill level.
They come to learn. They don't want to throw rose petals at you because you're a 'real pro' - they want to become pros themselves. So, if you call your video 'cell shading' - teach them how to cell shade. Don't waste 20-40 minutes of their time on your monologues about artist's hardships, your ex girlfriend or other irrelevant things.
5. Do not hide your 'secret techniques'.
It looks very childish and dumb when you show your watchers a line art, then tell them 'And now I'll apply shading and after effects, but I'll skip that part'. Then your video 'fades to black', and ta-dam, the awesome super-art is ready. Stupid. Lame. Don't do that. If you're so afraid of 'young talented artists' who will come and take your job - why bother recording tutorial videos? Go to your Basement Fortress of Solitude, knowing that you're awesome, and that no one will learn your secrets.
6. Don't hide _all_ your stuff behind the Patreon pay wall. Don't be an arsehole. Yes, you have to eat and pay your bills, but you won't starve to death giving out one free art/tutorial per month. There are numerous poor art students and beginners who literally have _no_ money to spare.
By the way, I don't like 'modern' Patreon, because people distorted its purpose with their greed. Instead of genuine support, Patreon turned into another money-making site. Nowadays it's just another net shop, where people sell their stuff for money. No more 'I'm a beginning traditional media artist, and I need a new set of brushes - please help me to collect enough money for that'. Ehh, people, you've ruined another good thing.
7. Don't discourage your watchers.
I saw several arseholes who made that on purpose. Like 'Oh, you know, being a pro-artist is a hard life. Yeah, not everyone is ready for all that difficult stuff. Besides, there are almost no vacant job positions, so you'll end up jobless anyway' I strongly disrespect such individuals. People come to you to learn how to draw - not to listen to your 'I'm so talented and you are not' sh*t. Yes, it's hard to be an artist, but it's not even close to all that gloomy crap you describe when you tell people about your job to scare off future competition. Don't be an arse - be honest. And remember that your experience and your opinions are subjective. There are many artists out there who are happy with their lives.
8. Don't use your 80$ copic marker as your d*ck extender.
It reminds me of this 'famous brand' thing, where there's a list of 'premium-class stuff', and you are considered cool if you have something from that list. Don't be an idiot. Skill and experience make an artist great, not his/her fancy 100$ sketch book. Don't misguide young artists by promoting this crap.
9. Mind your attitude.
Don't behave yourself as if you're mortally tired of all your watchers. This attitude is insulting and it can discourage a beginner. Your skill level doesn't give you permission to treat less-masterful artists like sh*t. If this 'teaching routine' really annoys you - drop it. Don't pour your irritation on innocent individuals just because you're tired and have a deadline coming.
10. More useful information, less personal remarks.
Your watchers don't want your stories - they want to learn how to draw. If you want to tell them about your awesome dog or about your new PS4 - record another video and call it 'Cool stuff I want to tell you about'. Leave all irrelevant information behind when you record a tutorial video - give people clear descriptions, short, useful advices and other good information.
Now - back to inking.