I also wrote a post on why I think that using lesser used tags is better than using the big ones.

What you can do is simply type any tag at the end of: https://steemit.com/created/put_tag_here

And you can see how many posts are shown. If there is a good number but not too high, I'd say use it.

Still I think that adding 1 or 2 main tags might help you get some big reach and if you're lucky you might get trending in these and it will surely pay out.