Experiment with volume and pitch to find a place where cracking is less of a problem. Excitement in you voice will be your biggest problem because you will be all over the scale and bound to pass through the area where your voice cracks. This is the reason why some teen boys talk in a subdued voice when their voice starts to break up. I don't recall it because I had enough problems in my life, but my mother said I was in that stage for a long time, possibly because my voice took such a huge drop and the final voice was nearly useless other than for monotone speaking.
