Acoustical treatments
The fiberglass pannels are a good idea, but consider the current acoustics of your room before making changes. Walk around the room, clapping loudly. If you hear a lot of echos than that is a bad sign.
Furniture and construction materials can make a big difference. Carpet or rugs on the floor, bookcases, couches with fluffy pillows, heavy drapes, etc.
If you have already done these things than pannels are the next step. Since it requires large treatments to accound for bass modes in your room, experiment with sub placement or consider a sub with a built in EQ to help correct the low frequencies.