Women and older adults typically prefer a warmer setting. Men generally prefer a cooler setting. If the group is mixed, consider setting the temperature in the cooler range and hanging some inexpensive shawls or sweaters on a coat rack in the back of the room. That way people who are cold can cover up without having to adjust the room temperature. The physical atmosphere can have a dramatic impact on your attendees.
Houseplants are also effective and can be used many times.
Smells are also important. Burning lightly scented aromatherapy candles can reduce stress or mask annoying food smells. Sound can also impede the learning process. Sound bleeding from adjacent meeting rooms is very disruptive. Always ask the convention service manager who will be in the room next to yours.