A clean vocal recording is essential for making a good demo. You don’t need to hire a recording studio, but you need to have at least a decent home recording setup. Please review these basic instructions.
You’ll need recording software such as Apple GarageBand or Logic. Learn the basics such as setting the proper recording volume to avoid distortion. Record in 24 bit and save your files as .WAV.
Work in a quiet room free from the sound of lawnmowers, television, kids and other background noises. Carpet is better than a wood floor, and wear socks not cowboy boots. If you live in a noisy neighborhood you might need to record in the middle of the night.
Put the mic on a stand and don’t touch it while singing. Use a pop screen in front of the mic to eliminate explosive sounds from your lips. Don’t get too close to the mic, stay at least 8-10 inches away.
The only sound going into the mic should be your voice. Music should only be in your headphones and not so loud that it is picked up by the mic. Inside your headphones you should hear the music and your voice together. In the room only your voice is heard.
Use a decent microphone, not the built-in microphone on your phone or tablet, or the one attached to your earbuds. That’s just for phone calls.
Don’t record with reverb or other effects, just make a clean track that we can add reverb to later.
Here’s a good video on the subject.