Things are pretty weird out there right now, and there are all kinds of reasons why someone might be concerned about their online security. A useful concept here is threat modeling: if the NSA/GRU/Mossad wants to access your devices, they can probably do that. But you can mostly thwart the regular police, or your employer, or a stalker-y ex, (or at least make things much more challenging for them.) Make sure that your devices are free from spyware, and be careful about what you send over text and email. Signal can secure a message in transit, but that won’t help you if you are messaging a cop, or someone with a compromised device.
How to: Get to Know Android Privacy and Security Settings
Really Basic Digital Security Zine (PDF)