Do you have brochures printed, menu possibilities from the foods you prepare, your new seasonings described?
Create a portfolio of these brochures and description sheets and include a cover letter about why you decided to start a catering business, your credentials esp with food and business, if you are going to target a particular section of the market (e.g., only to corporations) or will cater to anyone, a price list. Of course, in the cover letter there will be no spelling or grammar errors, it will be enthusiastic and charming, and it won't be longer than a page (since you will be including the rest of the info in the portfolio).
Begin to write the letter and post it, so we can pick around on it.

I LOVE to write and help with cover letters!