Start with a mild compression setting. Use a threshold of –10 dB, a ratio of 4:1, an attack time of around 10 milliseconds and a release time of a half second. Send signal through your compressor, and watch the gain reduction meters on your compressor to see how much the signal is being attenuated. Set the gain to compensate for this.
Compare your audio signal before and after compression (most compressors have a bypass switch for exactly this purpose). You should hear a fuller, more “present” sound. Compression tends to bring things forward in the mix, making them sound like they’re right in front of you. The more compression you add, the more noticeable the effect becomes.