It also depends on the amount of content in the hub. An in-depth hub of 1500 words justifies more tags than a 500-word hub. For the former, I can see up to 40 (in some cases, perhaps more) could be relevant, but in the case of the latter, I wouldn't use more than a dozen or so.
I always use more than 4, but rarely have more than 20 even in longer hubs. I would go with Maddie Rudd's advice since she is a HubPages staff member. Marissa's advice is also relevant-- especially about careful consideration of the automatically generated "suggested tags". I always leave at least half of those unused.
I just noticed your Hubs are very short, so you may find you're limited in how many tags you can use. Actually most of them are too short compared to the average Hub. Personally I'd be combining some of them, you'll find you'll do much better.
Thanks for asking the question and for all the great answers. Welcome to HubPages, it is quite the learning curb but I have found that there are quite a number of 'old hands' that lend themselves to assist us in our first fumbling steps. It is a great place to be.
I was always told, that when creating a web page for seo purposes that the optimal number of tags (keywords)for each page should be around 3-5, but be very specific researched keywords to the topic written about.
I know we are all here to make some money, but having 10 ads on a page slows down loading time to such an extent that readers just don't have the patience to wait for a page to load. So they click away without...
Had never done a “sales” hub before so decided to try. Have tweaked and tweaked this hub but it still keeps on being not featured due to quality. Getting a little T’d . . . http://geminifox.hubpages.com/hub/Green...