Listen to current jingles. What techniques do they use? What sound do they have? This will help you write your own jingles.
Learn the tone of the product and ad. Is it a fun, happy-go-lucky ad or a serious commercial about a disease? You want to match your jingle to the tone of the ad.
Write a simple phrase that sums up the product or ad. Example: "I'd like to buy the world a Coke" was a hit in the 1970s for Coca-Cola, while Wrigley's Doublemint Gum later used, "Double your pleasure, double your fun." The slogan might even be provided for you by the company or ad agency.
Write additional lyrics if the ad will have time. Keep the lines short and related to the tone of the product and ad.
Write a vocal melody for the words you wrote. For a successful jingle, this melody needs to be catchy so listeners will remember it.
Write music to accompany the melody. The music should fit the tone of the ad. For example, an ad with revving motorcycles might benefit from heavy, distorted guitar, while an ad for a hospital is more suited to piano and cello.
Play your jingle for a friend, family member or musician. Get feedback on the quality of your jingle. Make changes based on suggestions, if you agree.