1) Clear cookies/history/cache/everything from your preferred internet browser.
This is done slightly differently on different browsers.
On firefox: go to history (top header bar), clear recent history, ensure all history is checked, clear now.
Chrome: chrome (header), clear browsing data time range, all time/clear data
Safari: history, clear history, all history, clear history
Googling how to clear internet history, or cookies, or cache (all meaning the same thing) for any other internet browsers brings up pretty stepwise instructions.
2) Entirely shut down all programs, install any timely updates, and restart the machine.
Really. This might seem excessive, but better safe than sorry. While updates are essential for computer health, making sure you're using the latest version of your internet browser is particularly helpful.
3) Communicate in real time if there are problems: questhelp@austin.utexas.edu
Certainly, check with your professor before the exam starts if this is allowed, but if there are problems, we may be able to resolve them quickly and get you on your testing way. (If being proctored via webcam) Ensure you can see yourself in the live feed video box (if not, specific troubleshooting for this here).
4) Answer questions as you go through (knowing that you cannot change them after hitting 'submit answer')
That is, don't wait until the very end to put in all your answers. It leaves you in a bad spot should something go wrong, and provides no feedback for us that you are able to submit answers as expected.