Email: [email protected]
This is the easiest way to contact me and usually results in the quickest reply!
I'm fairly active on Twitter—even though I don't post a great deal—so if you @ or DM me then you're likely to get a fairly swift response (though not as fast as email).
Signal is an awesome and secure instant messaging service that works well both on mobile (iOS and Android) as well as on your computer/tablet.
If you already have my number then you will be both able and welcome to contact me via Signal. If you don't, and would like to do so then please do ask and I will likely be able to provide you with my number.
Also, in case you didn't know, WhatsApp uses the Signal Protocol.