The recording space is just as much of an important piece of equipment as the instruments, the software etc. The idea is to have only the sounds you want entering any recording microphone(s) in the space. If you are choosing to DI (Direct Input) then this point becomes mute. Most of the time microphones will be used so we will continue assuming this. One of the key concepts to consider is reverberation or decay in your room.
Reverberation
Reverberation is when sound is reflecting of surfaces within a given space causing echo until it finally decays and dies. If you make a loud sound in a room (say.. a snare hit) and the room has a lot of reverberation then your microphone will pick up the first snare hit and then the first reflection, second reflection, third reflection etc until the sound is absorbed entirely by the surfaces in the room. This may very occasionally be a sound you desire but more often than not you just wish to capture the initial sound and then add effects during the mixing stage.
Acoustic Treatment (Reducing Reverberation)
To reduce reverberation or decay as it is sometimes referred to the room should ideally be lined with absorbent materials such as carpet, heavy curtains, foam, rubber, blankets etc. This does not have to be an expensive exercise, you can pick up old rolls of carpet or carpet underlay at your local recycling shop. Egg cartons have also proved a classic favorite in budget home recording rooms due to the sound being absorbed in the divots where the eggs would usually sit and the cardboard material. Acoustic panels are also an option, but it is an expensive option.
The reduction of reverberation (decay) in a room will ensure a better cleaner signal being captured by your microphone(s).
One of my favorite videos demonstrating the difference acoustic dampening/enhancing can make.
Thanks for reading.