You can create a trigger that looks for key words or phrases in incoming tickets, then adds a custom tag and sets priority. This enables you to give urgent tickets attention first (for example, a customer that cannot log in to account).
To do so, use a trigger for rules based on ticket updates and text.
You can check for both subject text and / or comment text. Note that when the ticket is first created, the comment text will also check the subject.
Now apply your actions:
And you should be done.