If you sense, or actually know, that you are about to be fired you should take a few steps in advance of that notice. First, get you resume together and start looking for a new job. Second, make sure you clean out your work computer / laptop of any personal information it may hold. Third, make sure you have all of your contacts and other personal non-confidential information. Fourth, make sure you take home your most important personal documents and items in your office so that they do not get lost if you are escorted out.
Fifth, if you have a contract or offer letter that assures you a certain level of compensation or bonus it would be a good time to review your documents and understand your rights. Finally, make sure you have a copy of all relevant documents related to your employment at home such as the employee handbook, employee code of conduct, company stock option plan, your offer letter, your employment agreement, and/or any emails that support any claim for compensation or which might give you leverage to negotiate severance for yourself.