
This is easy to do -in fact I'm just doing it with my pup. :) It's really simple and you don't even need a clicker unless you particularly want one, I myself never use clickers, I have a clicker word which is used instead.
Starting from scratch, you must first teach the dog what the click means. (That is either an actual click with a clicker, or a word used only AS a click and not in other situations.) Click, give the dog a treat. Click again, give another treat, repeat this a few times until the dog understand that the click means a treat will appear.
Next you can start training. When the tail is up, click. (Easiest to start this on the floor first, before moving to the table, as the tail is likelier to be up when the dog is on the floor.) Remember the reward must always follow the click, never click without rewarding. The good thing though is that it doesn't have to be as instant as the click. The click means the dog has done right and a reward will follow ASAP. Hence much easier than to get a treat out as soon as the right action is carried out.
If the dog stands nicely but doesn't have the tail up, no click. The great majority of dogs (and Paps are SO clever!) will soon try to work out what it was they did that earned the click. As soon as the tail goes up again, click. It's just a question of repetition. Tail down, nothing happens, tail up, click and treat.
Good luck!