Make sure you are standing properly and without tension.
Do the exercises recommended in "How to Prepare Your Body for Singing." (See Related eHows.)
Close your eyes and take a few deep breaths to prepare yourself mentally for singing.
Consult "How to Do Breathing Exercises" for help on how to breathe right.
Be alert and listen carefully.
Say, Ma-Me-Mi-Mo-Mu, letting your breath flow evenly.
Make the transition from speaking to singing on the sounds of Ma-Me-Mi-Mo-Mu as described in "How to Do Vocal Exercises."
Sing on just one note that is comfortable for your voice range.
Listen to evenness of tone, volume and pitch on that note.
Make the sound flow evenly in a "bow stroke": (Ma...Me...Mi...Mo...Mu...)
Continue with the exercise and find the sounds you enjoy most. Use those sounds as models for the rest.
Sing Ma-Me-Mi-Mo-Mu on five different notes within a small range up and down the scale. Starting on the note C, that would be Ma = C, Me = D, Mi = E, Mo = F, Muuuuu = G-F-E-D-C.
Try not to force the sound in any way. Don't waste breath; focus is what you're after.