Not OP, but I am a nationally qualified running coach (in my spare time outside of my day job). I have run all sorts of distances from 5k park runs to 100 mile and above ultra marathons. I have made every mistake in the book and helped quite a few people avoid the same mistakes.

To keep things simple with two easy to follow steps:

1. Tall posture, imagine a balloon is tied to the top of your head and is pulling you upwards.

2. Download a metronome app to your phone and set it around 170 and in time climb up to 175 180 if it feels ok. You then want to time each foot strike to a beep. This will cause your stride to narrow and discourage an overstride. When you overstride the foot extends forwards and the force of landing gets absorbed by your knee / hips, which is inefficient (its almost like applying a break) and it can cause injury. Running at a high cadence tends to make you ligter on your feet and encourages a good foot strike (under the cartridge of the hips), landing in this way benefits from the elasticity we have in our tendons and you get a certain amount of energy return from this.

This video describes it very well and the runner has beautiful form. Just don't try to take it all in, focus on the cadence 170-175-180 rhythm and get that right first

https://www.youtube.com/watch?v=zSIDRHUWlVo