This is always a tough question due to the fact that each website is going to price their ads differently. As a general rule we suggest that when you're pricing your inventory for the first time, you should come up with a price that you feel is as low as you're comfortable with so that you can get some deal flow coming through. This will also allow you to see how your ads are performing and you can then adjust your prices accordingly. Your first goal shouldn't be to make as much money as possible from your ads, it should be to create a high demand for your ads and to prove the value of your audience to your advertisers.
Do not be afraid to ask some advertisers what they usually expect to pay for ads on sites that are similar to yours. Most advertisers will be more than happy to talk about it with you and as you get more information about the pricing of your market you can test different price levels and go from there. Just like with selling any new product, it's a learning process that will take some time to perfect, but once you do you'll be good to go.
As far as tenancy (week and month pricing) vs. CPM (cost per thousand impressions) goes, a general rule that you should follow is that if you are a new website with not too much traffic (less than 1 million pageviews/month) you should probably stick with selling on a tenancy basis. It will make it way easier for your advertisers to understand, which is always a good thing. If you have a ton of traffic and you feel like your advertisers are more experienced with buying ads on a CPM basis, then go for it.