The following will give you some guiding principles to help make this approach work. For the most part your goals should be to reach high level people in small to medium sized firms. This includes firms that are growing rapidly, bringing out new products, forming new divisions, acquiring other companies or reorganizing. These companies need good people, often from other industries. They are free to make decisive moves quickly.
Large corporations are the least likely to respond.
Get across your benefit proposition. It must be an accurate, concise and easily understood description of what you can do. It has to hold the promise of tangible value on a scale large enough to warrant an investment in you. In that initial communication you need to establish your credentials. Mention specific results you achieved in the past.