Overcoming the echo bare walls and floors produce takes a little effort but is not difficult. When rock and roll pioneer Buddy Holly had his garage studio, all the walls were covered in fence wire and stuffed with chicken feathers. A much easier solution is line the walls and floor with thick blankets. Thick fabric material will absorb sound instead of reflect it and create the echo as sound bounces from hard surface to surface.
Another sound absorbing material that is relatively inexpensive and comes in large volumes is pink fiberglass insulation rolls. The only caveat to using this material is making sure no one around the material is sensitive to fiberglass dust. Ideally, the fiberglass should be covered with blankets to make the garage safer and better at absorbing sound.
When a microphone or guitar string pickup receives sound from an electric amplifier there can be feedback. The sound circulates through the sound system and produces squeals and other distracting noises.
When setting up the garage studio emphasize that volume is not as important as sound quality. Adjusting the recording levels can compensate for lower volume. When the amplifier volume is lower the sound is not as likely to get picked up by the microphones and feedback is reduced or eliminated. Another idea is to direct the amplifiers in different directions. Again, the recording system will receive the sound no matter the speakers' direction. When the amplifiers project sound in different directions (preferably toward the blankets), the incidence of feedback is much less.
Unlike electric instruments, the human voice must project acoustically. It's not possibly to plug a wire into a vocalist and record directly from the source. Recording the voice is not very difficult but eliminating some interference will produce a better sound.
Always account for the vocalist's breathing. Air coming from the mouth and nose can cause static or rustling noise at the microphone. A windscreen works well to allow only sound and not air to hit the microphone. Two layers of pantyhose mesh is ideal sound screen material. Stretched over a round metal ring cut from a large can and held in place with a rubber band, the mesh will filter out all air and sound passes unobstructed. Place the mesh ring on a stand between the mouth and microphone. Alternatively, the vocalist can simply hold the mesh ring in front of the microphone on a stand.