Supermarkets are actually very difficult businesses. They have small profit margins, but very high product turnover. Supermarkets basically survive by selling a lot of product and making a small profit on each item. Competition is fierce and the price differential slim. A marketing plan should focus on getting customers into the store, and hoping that they will buy more than one item.
Since your question is a little vague, I would suggest choosing a product for which the profit margin is a bit higher. It might be a product acquired at a larger discount than normal. Then, you will be able to lower the price and advertise a lowered price. Since most people buy more than one item at a supermarket, you can make a higher profit on other items the person buys but you have given them the incentive to get into the story.
You can create a display for the product, and include other items that are similar and have higher profit margins near it. Customers who came to buy that one product may also buy the other.
Otherwise, general supermarket marketing is fairly typical. Generate colorful displays of products you want to sell fast. Discount items with high profit margins, and place impulse items, such as bakery items, fruit and junk food, in aisles and next to the checkouts.