1995 Mercedes Benz C230 Car BAttery

Check the obvious first, make sure there are no accessories or interior lamps staying on. Especially the glove box which is often overlooked. Also check the trunk lamp, if the trunk lid contact is staying open the red indicator on the release button will remain lit.

Beyond that you'll need at minimum an ammeter/multimeter to see the actual amount of current draw, then you can start systematically opening circuits until you see the draw go down.