How to correctly use a whisk?
Use a larger bowl than you'd think (or less starting product); you want your product to be able to move around. Hold the bowl on an angle so your whisk can shear through the liquid as much as possible. Other than that, you want to go in a fast circular motion, dipping in and out of the liquid in order to incorporate air.

Only way to avoid the fatigue is practice. You should see one of our prep cooks! She used to be patissier for a very rustic chef--no electric mixers in that kitchen. I've seen her whisk meringue by hand and then move on to making aioli without blinking. Girl's got pipes I tell you.