Topic: How many tags should I use

So, I've recently been contacted by an artist for whom I sometimes post things for. They were upset with me about not adding proper tags to my posts and said that their artwork doesn't do as well when not tagged properly. so my question is, what exactly is proper? have I not been adding enough tags to my posts this whole time? why didn't someone tell me sooner?
now I know the clear answer here is "add as many tags you can think of, ya dummy" and I know that, but I honestly feel like I add a very adequate amount of tags and I always remember to tag the artist of course. But obviously I'm doing something wrong considering I was just directly contacted by an upset artist, which is something I never wanted to happen. So does anyone have any advice on what I should do?

Updated by Mairo