Ok first of all this is what works for me, it may not work for you but it's worth a shot.

1. Breathing
Obviously breathing is usually the biggest recommendation, but there's a breathing pattern I follow that helps me. Breath in till your lungs are full, count to 4, breath out slowly. 

2. Asking yourself "whats the worst that can happen"
Realistic thinking helps me a lot, cause a lot of times anxiety is over things that don't have a big impact, like for example, a grad on a test, or what's gonna happen if you trip infront of people. Realisticly yes, it's embarrassing, but the worst that'll happen is people might snicker, or you might have to work a little harder on the next test. It's not the end of the world, and chances are people will forget about it by next week.

3. Realizing when you're over thinking
Catching yourself over thinking can help you stop over thinking. For me it's like pausing a show, I'll be over thinking, the drama is rising and rising, but then I realize "wait a minute, is this a likely scenario?"

4. Realizing it might be coming from someone toxic
I know it's hard to cut people out of your life, but sometimes it's for the better, yes they might try and guilt trip you, and yes they might try and make people think less of you, but you come first, your health comes first, if anyone tries and convince you you're wrong they have no place in your life.

Those are some things that help me and hopefully it helps you too. 