Granted it has been ~7 years, and I was searching for major $$$ to head to Spain, let me throw my 2 cents in.

For starters, figure out where and when you will be racing, use this to sell the 'exposure' you can give a potential sponsor. If you have a closed trailer, sell that as a moving billboard by showing all of the miles you will be travelling, and where the trailer will be seen.

Second, accentuate the positives yourself and your team can bring to the sponsor; i.e. a presentable appearance, competitive representation of the product (winning), and knowledge of the product and it's effect on your performance (if applicable).

The more you know about the potential sponsor ahead of time, and i'm not simply referring to "oh, yeah you guys sell shocks", the better off you are. Go in understanding the company as a whole, why they are positioned where they are in the marketplace, and where you fit in.

I don't want to overwhelm you, so I'll stop there. If you take one thing away from this, be confident, and know what your selling.