Using a clicker not only helps a dog learn new tricks, but the very action of working with and teaching your dog these tricks puts you on top of their priority list. This will help (the more you work on it) for times when Fido sees a squirrel in the yard, or a bike rider passing by.
This is one version of a clicker:
They come in all sizes and colors.
Here is a video about clicker training. When used correctly the clicker works wonders for basic training. The dogs and owners in the video have passed basic, and are now working on 'super skills'. If those things are possible, sit, come when called (the first time), and stay should be no problem. Right?
Everyone gets frustrated sometimes, what helps me is going back a step. Refresh what they know. Boost your confidence, and theirs. And if need be, take a breather, come back to the command later.
Remember, the clicker is only used to tell the dog they DID or are getting closer to DOING the right thing, not to lure them, that is what rewards are for! Once you are confident your dog is aware of the action that will get her a reward (treats, love, praise, toys) you can add the command word, such as "Sit".
Rule of thumb: Rewards must come after the clicker, but the clicker does not have to come after the action (the reward alone is okay).
Start today with charging your clicker. By next week both you and your dog will be loving the outcome of your training sessions!