Relax. Allow air to flow freely into your nasal cavity and pretend you are singing while sedated or very tired. Relax the muscles in the jaw, throat, tongue and nose, and allow your sound to be as strong or soft as you would like. Try both loud and soft singing to practice relaxing with both styles.
Focus on your breath support. Draw deep breaths and sing from your diaphragm. To practice this, lie flat on the floor, facing the ceiling. Breathe normally. You will notice your stomach area expanding, whereas the expansion is higher in your chest when you're standing. Breathing deeply from your diaphragm will give you a clearer tone and more vocal strength when singing.
Concentrate on the shape and sound of your vowels when singing. Focusing on vowels helps you sing from the diaphragm and thus produces a more pure, powerful sound. Enunciate your words so each has a specific beginning and end. Thinking about the words you are singing and how you are pronouncing them will relax your nasal cavity.
Practice singing while focusing on sending the sound through your throat, mouth and nasal cavity and out to the world. This balance of sound will allow you to sing clearly.