You could write articles targeting higher value keywords.
Mesothelioma and life insurance keywords have a high payout, if your site is already drawing traffic and you don't need to wait to rank for these keywords, it might help.
I'm really not sure what high value keywords are in Vietnamese, if you could somehow convince the people bidding for spots on your site to pay more, then you will get paid more.
Also, you have lots of room for more ads. More ads would probably lead to more clicks.