There may be a few steps to take if live preview in brackets is not working.
1. You should make sure you have the correct browser for the live preview (I'm not 100% sure if you need a specific browser, or if it opens a browser for you, but I use chrome).
2. You can look on there website for what suggestions they have in case something is not working.
3. Did you save? Many times I have been frustrated by live preview not working only to find that I hadn't saved my work.
4. Are you trying to perform the live preview on a CSS document? If so, then you should perform it on the main HTML document of the website (or the game).
5. Make sure that there are no problems with brackets or your computer. These can cause unwanted variables to stop you from seeing your live preview.