1.) Plant your blade fully in the water before you start to pull
Every stroke should follow this guideline. If you're not planting the full blade into the water, it makes sense that you're not getting all of the power from the stroke. This may sound like a big "duh", but it's easy to make bad stroke habits early on in your paddleboarding.
Keep that paddle in the water during the entire stroke as well. You'll find that not only is it a better workout, but you'll also move faster and have a lot more maneuverability down the road by making good paddling form habitual.
2.) Always assume the ready position when paddling.
The "ready position" allows you to essentially be ready for anything. It's hard to know when a rogue roller, or small boat wake will sneak up beside you and send you swimming.
Keep your feet shoulder width apart and your knees slightly bent to maintain a ready position. This way, when you get caught off guard, your knees can keep your balance where it needs to be, and your new hair-do looking classy.
3.) Use your core muscles for all your strokes.
If you don't know what your core is, it's basically the midsection of your body. On the other ends are your arms and legs (I went to college). I say all that only so you know to isolate your core when paddleboarding and use it for the bulk of your power.
Do this by bending your knees slightly and allowing your abs and back to pull you through the water. Your arms are simply there to hold the paddle and control the stroke.
Paddling with your arms can potentially hurt your back, so be cool.
4.) Keep your board quiet in the water.
A great way to tell how you measure up is to notice how "quiet" your board is as it glides through the water. If you're catching a lot of wake from side to side, your paddling is too tense. Lower your center of gravity and engage your core to keep things smooth.