You can start out by choosing a watch face that isn’t animated. This way it won’t sap your battery as much. Try lowering the brightness a little or turning on grayscale mode. These methods may be helpful but if you need a serious boost in battery life, take a look at the Reserve Strap.
This strap recharges your Apple Watch by Micro USB and is water resistant. Even better, it’ll add 30 hours to that energy-dependent device of yours.