Once you know you are “mixing” your voice, what is next? Is that all there is? Well, certainly not. Mixing is a good start, however!
The ability to mix your registers and sing well in your middle voice will set you up nicely with the coordination for safe and healthy resonance. But there are other very important factors such as breath control (airflow/volume), tone (vowels), cord closure (consonants), posture, and more to take into account. All these factors need to work in a balanced fashion to achieve good results. When one over-rules the other, the voice (throat) and body will likely try to compensate, thus causing strain.
Here is an exercise that you should do everyday to work your vocal cords in your mix. http://www.youtube.com/watch?v=bTHnsyCEsHk
Let me know how it went for you!