The most affecting factor is your search engine rank.If its high your cpc increases.Because if your ranking is high,google thinks that you are giving more relevant content to reader.Some website have very high cpc like 10$ per click even they got 10 clicks a day,they earn 100$ a day.And some have 0.03$ and subsequently earning is also less.
When you start website,start it with a single keyword in mind.Keyword should be of high traffic and low in competition.If your click is generated from country like India,Pakistan,Bangla desh or some Asian poor country,then cpc is low as compare to country like U.S.,U.K. and developed Europe countries.
Some people may take use of AdWord campaign to increase visitor.If you are earning say 1$ from each click.If you submit bid of 0.5$,don't think that you are in profit of .05$.Its not necessary that every impression you are getting will be converted in to click.If you are CTR is very high then its possible up to certain extend.So always try to increase your search engine rank by doing proper SEO.