My site has about 250,000 page views per month and has very highly targeted niche traffic. I'd like to sell banner advertising but don't know where to start. Is there a tutorial/ebook or something available ??

My main problem is what terms I should have - how much I should charge per month/views, etc.

Any advice much appreciated.

This is going to be intersting, as i want to know as well..

how many uniques do u get a month?
whats the location of your average ur visitor?
whats there age group?
whats your niche?

Not too sure what you mean by uniques. I can't see that stat in Urchin. It equals about 20,000 sessions per month if thats what you mean. Age range is 20 - 45 on average. Niche is musicians, producers & songwriters.

You could always try and collect geographical information on your visitors, and target local/semi-local music stores and present them with a Promotional package for buying advertisement on your site.
Or you can present the same package to major online record stores, music magazines, etc.
This promo package has to include as much information about your visitors that you can possibly dig up, and a complete outline of your webpage and your company. And examples or pre-built advertising packages.

how many uniaque visit per day?
what is your website?