As with other types of insurance, the general rule for liability insurance, from an insurer's perspective, is that your past claims history is a good predictor of your future claims. The greater the risk of future claims, the higher the premium. Good liability risk management is critical both to keeping premiums under control and avoiding losses.
Higher deductibles are another means of lowering premiums. Make sure that in the event of a loss, you can afford to pay the deductible you select.