Final answer:
Monopolistically competitive firms can increase sales volume by improving product quality, finding new uses for their products, and offering loyalty programs, thereby enhancing the usage rate among current users.
Step-by-step explanation:
An alternate way to increase sales volume is by enhancing the usage rate among users. To achieve this, monopolistically competitive firms could focus on strategies like improving product quality, innovating new uses for the product, and offering loyalty programs. For instance, if a firm innovates by finding new uses for an existing product, loyal customers might increase their consumption. Similarly, enhancing product quality could make the product more appealing and encourage existing customers to use it more frequently. Implementing customer loyalty programs could also incentivize increased usage by offering rewards for repeated purchases.