Wading through water is harder than walking in air because water is denser than air and creates resistance to our movements. Experienced divers move slowly, steadily, and deliberately to conserve energy and, therefore, gas.
Think "Be streamlined." Keep yourself horizontal in the water, and keep your equipment hoses and gadgets tucked close to your body. You will encounter less water resistance that way. Do not overweight yourself because this increases your drag. You will learn about correct weighting in an early practical session during this course. Nothing tires out a diver faster than swimming fast—or trying to swim fast—so relax and take it easy. Moving slowly gives you time to observe what is around you and enjoy your bottom time.
Currents can be a challenge. They are rarely uniform and usually stronger at the surface and around points of land and narrow passes. Swim across rather than into the current, or sink to the bottom (where the current will be less), making sure you don’t exceed your maximum depth.