As a trained singer, I myself do not yodel because it isn't good for your vocal folds. The reason being, a yodeling sound is created by a switch from chest to head voice very quickly. This puts a strain on your vocal folds because when you are switching registers so quickly the amount of air that is being pushed through your folds is un even and for an untrained singer the rapid change from head to chest could result "slamming" into your chest sound which will cause throat tension. I suppose for trained yodelers they are aware of there body and throats and know how to "properly yodel". I am not saying that yodeling is bad and it should never be doneIam just saying if you are a Classically trained, or aspiring Classical singer then it isn't really all that condusive to your voice's development. Butif you insist on doing this vocal activity, and have never done it before then one should start by proper warm up's. You will also want to work on delevoping a good rangeof sound. Strong Breath support is key, this will enable you to pop sound quickly from low register to high register using your diaphram instead of your throat. Next i would see about finding a vocal coach or maybe even a yodeling coach. Take it easy on your voice and good luck with the Yodeling!