It's not realistic to think a small diffuser will fill a large room with fragrance. Diffusers come in many shapes and sizes so note that when purchasing. If you want a bigger impact, consider using several reed diffusers in a room.

If your diffuser comes with a canister/vase for the oil to be poured be very careful. The oil can damage many surfaces, wood and granite and marble counters. Make sure to wipe the sides and bottom of the canister. You can use any glass vase or reuse another diffuser piece that you have at home.  We love to reuse and repurpose items. It is a nice touch to place your diffuser on a pretty coaster/plate which is a good safeguard too. Also the reed diffuser refills are often cheaper, so you can reuse your original vase or whatever you have at home that looks nice in the room.

We recommend you put the diffuser in a high traffic area (i.e. entry way, shelf in bathroom, family room). Your guest will notice the fragrance immediately.  Air flow will also help the fragrance diffuse into the room. So set on a table near a vent.

Your diffuser probably came with 8-12 reeds. You can place all the reeds in the canister at one time or you might choose to place half now and then replace later with the rest. The reeds can last up to 4 months, but all depends on the temperature of the room. When the reeds get over saturated they will stop working as well. What many people do not know is for the best performance of your reeds, you will want to flip them as they become saturated. This promotes the release of fragrance into the air. I always purchase extra reeds too so you can add some at any time to help the performance of the diffuser.