In most cake recipes, you would have noticed the step (usually after preheating your oven to the desired temperature) that tells you to prepare your cake pan - line your pan with parchment paper/grease your pan, etc.
Some recipes would want you to prepare your cake pan even before you start to measure your ingredients and some recipes include that step after the batter is prepared. But i would say it's best to prepare your cake pan before hand because once a batter is mixed, a lot of chemical reactions take place that could reduce its leavening power and hence produce less rise, so why delay baking?

