Check out the link for a few basic tips on how to teach sit. Besides whatever content I was able to provide to the authors on the piece I was excited to see that I was called out in THREE places with expert tips!
The basic premise: "To get your dog to sit, hold a treat in your hand, then move the treat up and over the dog's head. Allow the dog to follow the treat with their nose until their head goes so far back that they angle their back end down to try to reach it even further, eventually touching their butt to the ground."
A helpful tip on when to use the new command: "Consider waiting to form the association with the word 'Sit' until the dog sits consistently. Often, trainers will wait to associate a word with an action until the action is being reliably performed, lest you accidentally pair that word with an incorrect behavior while the dog is figuring it out. In addition, staying quiet brings down the energy so your dog can think more clearly. By allowing your dog to solve the puzzle on their own, you'll unlock more of its potential."
And a tip on one of the most important and often overlooked steps, bulletproofing the behavior: "Try repeating the training in a variety of different situations. Understanding the mechanics of a behavior is only the first stage of learning, so don't stop training just because your dog responds to a command to sit. To ensure the dog is fluent in what sitting really means, try changing variables, like being in a different room, outside, and around other dogs when you give the command."
One other tip I like to give on the subject is just to remain very quiet during this type of trick training. All too often people repeat the command over and over, like the dog will suddenly hear them and figure it out, even though they have no association with those words yet. "Sit, sit, sit, no, sit, sit." You can see I mention this above, but the added bit of advice here would be to just withhold the treat until the trick is performed. The punishment for not doing it then is simply not getting the treat, not admonishment from you. The dog should continue working at different ideas to see what gets the treat, you do not need to keep speaking, just be ready to praise when they hit the position and treat very quickly after.