Extracted from: https://support.twitter.com/articles/15367  

To post a Tweet via the web:

• Sign into your Twitter account.
• Type your Tweet into the box at the top of your Home timeline or click the Tweet button in the top navigation bar.
• Make sure your update is fewer than 280 characters. Twitter counts the characters for you! Remaining characters show up as a number below the box.
• Tip: Read about how to post photos or GIFs on Twitter, and how to share and watch videos on Twitter .
• Click the Tweet button to post the Tweet to your profile.
• You will immediately see your Tweet in the timeline on your homepage.

For those updating social media for HM (but also useful for colleagues working on other social media accounts)

Social media treatment: When posting updates, please remember to try to adapt headlines from the source, for example by inserting relevant (and known) hashtags, the publication and the journalist. On LinkedIn, please try offer a different angle – maybe pick something out of the actual destination piece. Also, do check the coverage email and ensure that client coverage is promoted in a timely fashion – do extend this to monitoring client feeds and retweeting relevant content.

Overall: The emphasis is on quality not quantity. Try to find information that is genuinely useful to our target audiences and offer a fresh spin on it.