Twitter
If I look through my current Twitter newsfeed, I see that every single one of the tweets has at least one hashtag in it.  Click on that hashtag to see more about that topic and what is happening.  If a hashtag is trending, you will see it on the left hand side of your newsfeed.  Can you add value to this trend?  Perhaps bring your business into the trending topic.   Use a maximum of 3 hashtags in any of your tweets.

Instagram
This is one platform you can use more than the 3 you use in Twitter.  But ensure that you are using your hashtags to your advantage.  For example, you are a Mercedes mechanic, you wouldn’t just use the hashtag #mechanic or #carmechanic, be specific and say #mercedesmechanic.  This way you will reach the people seeing a mechanic for their mercedes.

Facebook
Hashtags are not used as much on Facebook (or Linkedin), but when used it will help others follow you and your posts, as well as others.  For example, if you see a Facebook post with a hashtag – click on the hashtag and a new page will open with all posts with that # all being visible.  Trending topics can also be seen on your Facebook page news feed.

Pinterest
If you want to add a hashtag to your Pins on Pinterest, make sure they are added to your Pin description as otherwise they are not clickable to your followers.