The key to figuring out how to work the additional keyword into your description is understanding its role in the paragraph. The additional keyword is essentially a bit player, a supporting cast member that plays a part, but is not the star of the piece. That role goes to the main keyword.
Never disparage the additional keyword. Imagine that this bit player’s family has made a special trip to see it perform. Now, imagine that as the additional keyword takes the stage, the narrator announces, “While keyword is the best ever, steer clear of shoddy items like additional keyword.” No matter how small its role, cast it in the best light.
In addition, the additional keyword ideally plays a meaningful or logical part, no matter how minor. In other words, it is not just given a throw-away line: “Get additional keyword while you are at it…“ “Shop for great stuff, such as additional keyword.” If you use that kind of set-up, add meaningful detail about the keyword – adjectives, advantages, uses, etc.
Aim for a seamless segue. Do not just shove the additional keyword on stage with no set-up and no rhyme or reason for its presence. Generally it works well to introduce the additional keyword midway or later in the description. The additional keyword does not belong in the opening line or in the summary. That is where the main keyword shines. When the additional keyword starts the second line of a description, for instance, the audience loses track of who is the real star.
Final advice: Scan the list of additional keywords before you click the link to research your main keyword. Perhaps one or two already stand out to you. Then, you can look to see whether this keyword is offered by the main keyword brand, for instance. Never just assume that the additional keyword is a product or feature offered by the main one, either.
When you initially scan that list to choose your bit player, understand its relationship to the main keyword. Is it a feature? Is it a rival brand? Is it an accessory? Is it simply a synonym for the main keyword? Understanding that relationship goes a long way toward inserting the additional keyword in a logical way.