What helps me most is to find a comfortable rhythm, which is a combination of stride cadence and breathing. I’ve read advice on counting strides, and matching breaths to certain steps. It’s hard for me to coordinate all that so I go by feel. If you’re not feeling comfortable maybe try going slower.
When your legs don’t want to move it could mean that your muscles aren’t warmed up. You might feel better after taking it easy at the start of the run. Or your muscles might be tired from recent exercise. Either way make sure you’re hydrated.