This study examines how liquid electrical properties (conductivity and permittivity) and the frequency of an applied voltage affect electrodynamic forces on droplets in digital microfluidic devices. The study finds that forces increase with conductivity up to 10-3 S/m and decrease significantly above a threshold frequency that depends on conductivity. Numerical simulations and experiments show that low conductivity liquids are best actuated at low frequencies while high conductivity liquids can be manipulated at higher frequencies without reducing forces. These results help optimize voltage and frequency for generating the strongest actuating forces on droplets.