Measure the distance from your elbow to the tip of your middle finger. Pick out a baton that matches this measurement, give or take 1 inch. This length is comfortable for most conductors, though you can certainly try out different lengths to see if you prefer a larger or shorter baton.
Opt for a color that contrasts with your normal conducting environment. Typically, batons are made from pale wood to stand out amid a dark stage backdrop and a conductor's dark suit coat. However, if you normally conduct in a brighter environment, select a darker baton for better contrast.
Place the baton on your pointer finger until it balances freely. A baton's balance point is usually near the bottom end of the baton. Pick a baton where the balancing point coincides with your thumb and forefinger's natural position on the shaft.