Mine is simple, the same as for 2017, increased page impressions.
I have always done OK as far as earnings per page impression are concened and in 2018 I will make little or no effort to improve on that.
My major effort will continue to go towards increasing the number of visitors to my site and the number of pages for each visitor.
Smaller sites appear to be under huge pressure in 2017 and in my opinion, higher volumes of visitors is the key to survival.
This is all relative to any particular market. For example if your site is about mobile phones, you will need huge numbers of visitors to survive. If your site is about orange pyjamas then far fewer visitors will be needed for you to survive. There is a large spectrum in between.