What is the best way to determine the amount to charge advertisers per click/impressions?

You really don't need to do that. Most people use an "ad-exchange". See this http://en.wikipedia.org/wiki/Ad_exchange

I've used RightMedia in the past (now part of Yahoo).

[Source: I founded isocket - we power direct ad sales for the web's best publishers like Microsoft, Aol, etc.]

If your application is new and the traffic still modest, you should focus first and foremost on building your audience before worrying too much about ad monetization. And the typical first step is to throw an ad network on, which will take care of the pricing economics for you behind the scenes.

If you're ready to do direct ad sales, then some good starting rules of thumb for a smaller site are:
* $1-3 CPM.
* Double what you were making eCPM from networks like AdSense.
* Ask a potential advertiser.

We always encourage new publishers to start off with a price low enough that, given your audience, you are super confident you could spend an hour calling potential advertisers and at that low price SOMEONE would take it. Start there, repeat, move upward.

Make it auction-based just like Google AdWords, Facebook Ads and LinkedIn Ads.

Global digital advertising spending is expected to rise 17.1% to $327.28 billion this year, with Google and Facebook leading the pack when it comes to U.S. If you are not spending a lot of money on advertising and have opted not to run experiments with different audiences, ad sets and variations, and are instead focused on optimization, CPC advertising is likely a great option for your business. The average cost per click for Google Ads varies depending on your industry, business type, and networks that you run your campaigns on. The prices you end up paying for each click on Google can add up fast, especially if you do not keep a close watch on things that affect CPC cost. Like other types of pay-per-click advertising, Google Ads are placed through an auction process. While big ad budgets are always a plus, the Google Ads' process ensures a far more level playing field than you'd expect.
You can read more here: https://adespresso.com/blog/cpc-advertising-guide/
Besides if you do have any questions give me a call: https://clarity.fm/joy-brotonath