If you have a large budget it is easier, you just make a huge keyword list, sort them into relevant groups and test them in Adwords.
But if you don’t have the money to support that strategy, I suggest that you start finding the best performing keywords and start from there.
1. Start by making a huge keyword list
2. Split the keywords into groups that makes sense
3. Choose only the keywords and groups you expect most from
4. Make very targeted landing pages and keep testing them
5. Setup analytics with conversion tracking so you know what is going on
6. Make an Ad Group in Adwords for each of the groups you have chosen
7. Filter the traffic, in Adwords, so you don’t get traffic from places that don’t convert
8. Add the conversion optimizer (or similar bidding tools) when you have enough conversions (so you can focus on 1-4).
The most important is to find the keywords that is going to bring you visitors that want your product.
It might sound difficult, but it is not. You will be looking for longtail keywords of 3-10 words that have the intentions of buying your product.
Please comment or ask if you have any questions