You can face it head-on, overpower it, soothe it, or distract from it.
To face it try writing down exactly what it is that's causing your anxiety (what are you worried/afraid of). Follow each worry to its logical conclusion/outcome. Remember to eliminate this evidence when you're done.
To overpower it try power-poses for at least 10 minutes. This sets your mentality into a "superior" state.
To soothe it turn on some music, take a bath, breath deeply (in through nose, out through mouth), and, starting from toes and moving all the way up, tense and release each and every muscle.
To distract it try doing math you find beyond your abilities. Actually work on the problem. Make it your mission to solve it. Math isn't the only option, of course, but you want to avoid stress-inducing problems (like focusing on an upcoming meeting, presentation, etc.).
These are cookie-cutter techniques for stress management. For myself I've found that music is all I really need. I try to match it to the type of date I'm looking forward to having.