Ok, I've selected a bunch of CB products to promote, now what about keyword research?

First of all, I'm sorry if this question is a bit "noob" for many here but I thought I'd rather have the opinion of other more experienced marketers than dabble for days and days or worse, complete a whole campaign just to have the same results as 95% of others out there: nearly to no sales.

I think I've done a pretty good job in product selection: I examined each and every sales letter in my niche, looking for flawless and engaging writing and several calls to action, as well as credible testimonials, preferably at the beginning-middle of the page. I also checked products' history (stats, names used, continuity, etc) with CB Engine and CB Analytics beside CB Marketplace, of course. Gravity was not determining at all as it can be manipulated; I chose both products with high gravity (up to mid 100s) and low one (single digit). The main stats that I paid attention to were: Avg$/sale, Total$/sale, %referred, and date product went online. It would have been excellent to check %refunded for all products but I reckon that variable is not publicly available; what I did was verify that product price and Avg$/sale were not too different and pass the product if that was the case.

So now I have a bunch of about ten-twelve products and the next step is keyword research. I'm using G's External Keyword Tool and MS to start with and introducing the product's web address to get keywords, but so far the data is meaningless. How do you keyword research in this situation? I know it's not an exact science and it's actually similar to mining ore: you start with a general idea (root keyword) of where the gold is, and from heaps of mineral (keywords) only a little fraction is useful (long tail keywords with commercial intent).

Having selected the (CB) product(s) first, how do you approach keyword research?

Thanks a lot for your help