Both Human Made and the WordPress community use Slack as their real-time communication platform. As a result, I basically live on Slack.

There’s more to Slack than just “chat”, but you have to know how to own it as opposed to being owned by it.
Here’s how I got there.
1. Understand the difference between teams and channels
First of all, to use Slack properly, you need to understand the distinction between teams and channels.
Teams
Think of a team as a community. You can be logged in to multiple teams at the same time (i.e. your company, the WordPress community, the WordPress UK community, etc.), and join different teams with the same email address / username.
The question “Are you on Slack?” doesn’t make any sense unless the Slack team is implicit (different from i.e. “Are you on Skype?”).
Channels
Each Slack team has usually more than one channel, for different departments etc. This allows Slack users to read only the chats that are relevant to them.
Slack doesn’t allow channel arrangement in the left sidebar yet, but you can create your own hierarchical system (sort of). From the most important: starred channels & chats (for projects I’m actively working on, they appear on the top of the left sidebar); regular channels (I receive all the notifications for those); channels where @channel and @here are suppressed (don’t want to mute them, but still don’t want to be pinged for general announcements); muted channels (all the channels that are not strictly required for the work I’m doing).
2. Slack is not the right place for important discussions
Because of its real-time nature, any important conversation or write-up should happen or be recapped elsewhere, for example in internal websites that have a WordPress theme called P2. Websites with the P2 theme have a posting form right on the homepage, inline editing of posts and comments, real-time updates, and much more.

3. Use Slack asynchronously
Slack is often hailed as the saviour of internal communication as well as the destroyer of emails. Thanks to Slack, we don’t overfill our inboxes with countless internal emails, so we don’t have to keep up with different threads, mess with addresses in cc, etc.
In traditional communication, whilst emails are among the most effective asynchronous communication tools out there, chat, texts, etc. represent its synchronous variety. A team that works across multiple time zones can’t chat synchronously all the time, and as emails are out of the question, we need to adapt the chat and transform it into an asynchronous communication tool.
Do Not Disturb is the king
Slack allows users to set them on Do Not Disturb mode (automatically or manually). When someone is on Do Not Disturb, they won’t be notified in case of ping, but the system can be forced if the matter is urgent.

Generally speaking, it’s important that people can talk to each other even when the recipient is not around. If you understand you’re responsible for your own down time (setting yourself up on Do Not Disturb when you’re offline, not working, or in-the-zone), you’re giving others the freedom to get in touch with you anytime. It’s your responsibility then to deal with the message when you’re ready.
4. Always prefer public channels over private and 1–1 communication
When in doubt, always post a message where everyone can read it. Keep everyone updated on stuff that is not secret or private!
5. Do a routine decluttering
If you’re anything like me, you’ve been there: you’re in several channels, and some of them either ended up dead or lost relevancy to you and your job. Leaving channels when you’re not interested in them anymore means you have less stuff to catch up with.
6. Kill Slack when you need to focus
Which doesn’t necessarily mean quitting it. You can set yourself away, or activate Do Not Disturb, when you want to focus on something without being bothered.
7. Use Slack themes
Slack allows to customise the colour scheme of the left sidebar. Just head over to Preferences → Sidebar Theme and select an available theme, or enter your custom colour combination.
For example, this is a colour combination for WordPress:
#23282d,#191E23,#0073AA,#FFFFFF,#191E23,#FFFFFF,#46B450,#00A0D2
Bonus: is there a night mode?
Slack doesn’t have a night mode yet, but there’s a nice workaround for the in-browser version. Install Stylish for your browser (an extension available for Firefox, Chrome and Safari), and follow the instructions here.
External resources
WordPress communities on Slack – A collection of Slack teams related to WordPress (both country-level and non-local teams)
Slack on Product Hunt – Slack-related apps, add ons & collections.
Slack Themes – A collection of themes for the left sidebar.
11 Useful Tips for Getting the Most out of Slack, by the Slack team
An Incomplete List of Communities on Slack, by Angela Cois