Consider getting the Slack desktop app - either the native OS X / Windows one, or the Chrome app, which you can set up to run as a standalone app on system start up.
Write specific people @name
Calling attention to all subscribed to channel write @channel or @group
Calling attention in a channel/group to just the people who are online write @here
Make sure you're available in slack when online
Make sure to add a photo of yourself for your Slack avatar
In preferences, add your name as a keyword that pings you when mentioned (in case people forget to @ you when trying to get your attention)
There are a number of different channels you can join
You SHOULD join: General, Announcements, Engineering or PM, your Pod, your project channels
Consider also joining: Random, SOTD, QOTD, Onboarding
Announcements channel is only for announcements, not replies to the announcement, which you can do in the General channel. It's a one-stop channel for anyone who hasn't been paying attention to the general or other channels but wants to ensure they got any important or not-to-be-missed information.
There's a Slack Onboarding channel that you can use for any general onboarding questions if you think it's helpful.
Tips
Consider using the word "ping" to check on the availability of someone
Create a Google Hangout w/in Slack: /hangout (will need to authorize the slack app in hangout too)
Wrap your text in single asterisks for bold, underscores for italics, grave accents for code, and start the line with a “>” sign to make it a block quote. Formatting in Slack is similar to Markdown. see attached here.
To quickly bring back the last message you sent back to the text box, just press the Up arrow key.
Wrap output in three backticks (see backticks image below)