Chasing trends isn't a great strategy for most businesses, but you should still watch for social media trends. When properly leveraged, they can have a huge impact on your bottom line.
Be quick and simple: Hashtags and their trends are notoriously fickle. If you aren't in the conversation and creating your item in the moment, people will quickly forget and not care.
Be brand aware: That being said, don't jump on every trend and hope it may land. Many brands have made snafus in that area by aligning themselves with a hashtag they thought meant one thing but was actually saying something completely different. Consider keeping a list of the topics/brand messages handy so you can say, "How might this align with our message?" If you don't have a clear answer, hold off on posting that tweet.
Understand the spirit: If it is a lighthearted joke on social, match that message. If it is a more serious hashtag, you don't want to be silly and look out of touch.