Start with a treat lure to guide your dog into the behavior you want, such as "sit." Immediately say "Yes" or click a clicker when your dog does it and then feed the treat. Make sure  you go slowly enough that your dog's nose stays "stuck" to the treat. 

Switch to hand signal: Once your dog is successful with the treat lure every time, make the same movements without the treat in your hand – this will become your hand signal. Say “Yes” or click when your dog does the behavior and feed a treat. Over time you can change this motion to be more like what you prefer the final hand signal to be.

Add cue word: Once your dog is responding to the hand signal reliably, add your cue word before making the hand signal. Say “Yes” or click the moment your dog does it and feed.

Practice in different places and situations. This is where the real work is as your dog will need hundreds of repetitions. It really helps to track your progress in a worksheet. You will need to practice indoors, outdoors, in different locations, with different types of distractions and for some behaviors you will also want to practice duration and distance. 

If your dog struggles, make it easier for a few reps, make sure your rewards are top-notch, and don't mix in stuff your dog doesn't like (like asking for sit and then trimming nails).

Fade and vary your reward: Once your dog can do the behavior easily, you will start to use other rewards like, play, petting or access to favorite things (like going outside) and reserve food rewards for the very best examples of the behavior.