You really have to build and market your site around the products you intend to sell. A large part of this is effective 'On Page' SEO.
In other words your pages and indeed your website need to be optimized with the keywords people will be plugging into google to find the products that they are looking to buy.
If you target highly specific 'long tail' keywords then you will inevitably receive highly targeted traffic.
Don't fall into the trap of simply seeking the highest volume of traffic possible because more than likely the traffic that you get will not be targeted.
A trick is to target a single 'long tail' keyword until you rank well for it, then look for another highly specific keyword and work to rank well for that one.
After a time you will find your site ranking for more and more highly specific keywords. Although each keyword probably won't attract bone crunching rushes of traffic, you will no doubt find the traffic you do get will result in a lot more purchases.
The key I think is to identify and target a number of 'long tail' or specific keywords and rank well for them rather than to target a very 'general' keyword phrase in hope of getting it lucky with a large volume of traffic.
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