Tags tags tags. Tag! You're it.
Tags are awesome. They get eyeballs to your posts. People that may have a similar interest or are looking for whatever it is your post may be discussing. Tags also are what can earn you steem or palnet or whatever token you are looking to get.
So while overall, this is a great thing it is far too often abused and misused. I see it every day, people adding 5 10 I even saw 12 tags today on a post here. Guess what? Not a single tag had anything to do with the subject matter. One of several things will happen. You will not be taken seriously, you won't earn any of the sought after tokens or you will stop earning upvotes altogether and thus cutting yourself off from earning steem as well.
On the other hand, if a tag is appropriate by all means, use it. Who knows, you may even become a well-known curator or influencer in your tribes.
You can check https://steemit.com/tags for the trending tags. This will give you a clue as to what is popular, at least at the time anyway. Go out and do some research. If a tag fits use it if not, just keep walking. The community thanks you in advance.
As always, this is just my .02¢ YMMV