Google Ads is the baseline, in the sense that they will put your ad anywhere, except maybe on a porn site, but you'll make the least money with them versus another advertiser. A decent Google Ad rate is probably $0.15 CPM (CPM meaning per 1000 page views/impressions).
You're going to make the most money by privatizing your ad rates and getting clients that will pay you directly to display their ads. If you have the means, that's the best route. You can charge a pretty high amount depending on what you can negotiate. Making $1.00 CPM would be a great return rate.
There are a lot of other advertisers that will pay a decent amount, but they usually expect you to be a very specialized site, in the sense that you have a very narrow market. I was signed up with a second advertiser a year or so ago when I ran a video game site that would use Google Ads as a backup, and they would fill the ads at about an 80% rate, for around 0.30 CPM per ad on the page (we had two). So, it was an okay rate.
Now, getting to a reasonable traffic flow, this is where you really need an insane amount of traffic to make your time worthwhile. If you're getting less than maybe 250,000 page views per day, you're not going to make very much money. So you really need to find an idea that is going to attract unique traffic on a regular basis without you putting much time into maintaining the site. And if you get to the point where your site is nothing but ads, people won't visit them and they'll quickly get a reputation of being ******** sites that don't seem to offer anything legitimate. And 250,000 page views per day is a crazy amount of traffic. If I had to guess, I'd say Jazzfanz turns in maybe 10,000 page views per day, and perhaps up to 50,000 during the peak times of the year. With google ads and a low conversion rate (forums don't lead to a lot of effective ad impressions), I'd guess their CPM is probably like $0.10 to $0.15. It seems like it's a lot, but I hear Jason has to pay a bit out of pocket to keep the site up, even after the earnings from ads. Which is why, I'm sure, he appreciates any donations.
When I was running the video games site, I think I made $50 in 4 months with about 950-2,000 page views per day, and I did a lot of work to get that site launched. Needless to say, it was down quickly. But, I did get a very good programming framework put together and it gave me enough experience to be a professional, contracted PHP developer, so it was actually a good thing. Not to mention, I learned a lot about trying to make money on the internet. There's plenty of potential, but I'd say only about the top 0.05% of web sites actually turn a reasonable profit. Don't get too fixated on numbers. If you find yourself thinking about numbers too much, it's a sign that you're not making much money and you should spend your time elsewhere.