I used to get really bad anxiety and what helped me was a bit of basic CBT. I wrote down when I was anxious, why, rated it out of 10 and then what I did to try and get rid of it and then re-rated it. Sounds laborious and stupid I know and I thought so too before I tried it but it really helped. On a practical level it helped me identify what was working and what wasn't but it also made me be rational about it rather than just succumbing to blind panic. There are lots of CBT based books out there about anxiety.
Other than that I just drink lots of tea and go for long walks
