The amount you earn per click on ads varies based on the ads. Since each niche has different click values the amoount you earn will depending on what niche ads are running. For example credit card, loan and medical topics have high click values. So you could earn $1-3 per click vs say a music or recipe article which may only give you $0.08 per click.
We suggest you try focus on a niche but occasionaly add a little bit of everything to increase your chances.
if you only get 1 click a month for a medical article you might make $2 or 3 but if you get 20 clicks a day and earn $0.08 per click you would earn $37.50 for the month.
you must find a balance between value and volume