Before trying to make incense stronger, give the fragrance a chance to distribute through the space. Room size, open doors, fans, windows, and your own scent adaptation can all change how noticeable it feels.
Using more burning incense is not automatically the best solution because it also creates more smoke. A smaller room may need less, while a large open area may diffuse the scent quickly. Use incense only in the amount and manner intended by the maker, maintain reasonable ventilation, and never crowd multiple burning sticks together just to increase intensity.