iirc snowden has some opsec type guides and recommendations, but a lot of that is probably out of date now. No one would really know how to avoid them except the people who work at those agencies and know the full extent of their surveillance programs.

Continue as usual. Waste their time.

I’d get those sunglasses that have little mirrors in them so you can see who’s sneaking up on ya

I’d consider whether I’d done anything that warranted such surveillance. If I hadn’t I’d wonder whether, actually, whatever causes me to suspect I was under surveillance could be explained by something else (Occam’s Razor and all that).

There is the excellent InfoSec for Journalist handbook from Silkie Carlo and Arjen Kamphuis. The latest edition is from 2016 but it still contains valuable information and it covers a lot of topics. The handbook is no longer being updated which is likely caused by the disappearance from Arjen Kamphuis in August 2018.

https://beschermjegegevens.nl/wp-content/uploads/InfoSec-for-Journalists-V1.3-1.pdf

I also found this more elaborate book, a collection of articles, posts and lectures and a handy InfoSec guide from Arjen Kamphuis. The InfoSec guide starts at page 307 but is probably the same as the one linked to above.

https://beschermjegegevens.nl/wp-content/uploads/arjenkamphuis-infosecurity-small.pdf

It would be safest to not use any network communication at all. Also make sure that your convos are not being overheard obviously.