0. Unless you've been running for a long time or done some other endurance sport, your aerobic system is probably in terrible shape. Even if you are already a runner, it's likely your aerobic system is still in terrible shape. If your pace zones don't match up with your heart rate zones, e.g. you are out of breath no matter how heard you run and your HR shoots up the moment you start running then you need to improve your aerobic system. If you are stressing yourself on every run then you have a much higher chance of injury. On most of my runs I go <Z2, which is about 6.30 min/mile for me at the moment but could easily do a marathon at that pace and not be too stressed about it. I can breath through my nose at that pace and assuming I warmed up sufficiently, then breathing feels very easy and I can carry on a conversation with my running partners. Recovery feels almost instant after stopping. If your aerobic system is poor then you'll be dipping into anerobic territory which stresses the body a great dealand lengthens recovery time. I only work anerobically about 20% of the time. Teach your body to be a better fat burner, your aerobic system will thank your for it and you'll feel generally better overall in daily life. Learn about the aerobic threshold and the anerobic threshold. The secret to fast, injury free, easy running is to push your aerobic and anerobic thresholds as high as possible, so you can run fast whilst burning fat and not accumulating excessive levels of blood lactate. You can achieve this by doing most of your training below your aerobic threshold and the remainder at or above your anerobic threshold. Determining your aerobic thrshold can be tricky - some people say it's the pace you can run at when breathing through your nose. If you have a blood lactate monitor then it's the pace/HR when lactate starts appearing in the blood samples. It's maybe easier to do a metabolic test though. Read Phil Maffetone's book to learn more - it's a good introduction.
1. Make sure your form is good. The main things are: 1) don't overstride. If you overstride, you'll land on your heel instead of mid/fore foot and put quite a bit of stress through your legs. Instead, increase cadance and lower stride length so you are landing mid foot. 2) You see a lot of people running with their ass sticking out, which pulls centre of gravity backwards and makes running much more difficult - overstresses quads, shins and knees. Your centre of gravity should be directly over the foot in the stance phase. Try to make sure hips are forward and level. There's tonnes of stuff on the internet about running form. I think you can get most of the way there by increasing cadence and shortening stride. Running should feel like you are gliding over the road... People walking should be surprised when you beast it past them at 5 minute mile pace because your feet hardly make any noise when they touch the ground.
2. Make sure that all your muscles groups are strong and balanced, in pcarticular the glutes. Most people have weak glutes, specifically the glute medius, which will cause the knee to bend inwards when running, resulting in quite a bit of pain as it compresses the knee on one side and stretches it on the other. Many runners think strength isn't relevant for running but it really is. You need to keep on top of it and do strengthening exercises at least a few times a week. There's tonnes of blogs on the web which teach you the kinds of exercises you need to do. E.g. side leg raises, clam shells, squats, single leg dead lifts, glute bridge, marching bridge...
3. Recover properly. Any "tightness" after a run is probably because you've overworked some muscle group. Learn how to do self massage and maybe use a theragun or similar device. Cold therapy also helps. Try to sleep well (no alcohol before bed, no food three hours before bed, no caffeine in afternoon) and if you don't feel great or are ill then either don't run or do only active recovery that day. From experience you are way more likely to injure yourself on a day where you don't feel great.
4. Whenever you are going to do a hard session, warm up properly with some light aerobic exercise and mobility exercises. You want to make sure all the main muscle groups are activated and ready to go before you run. On slow days this is less of an issue. A hard session is anything above Z2. Always run at least 5 minutes in Z1 before starting any run. Alsways do at least 5 minutes in Z1 at the end of a run.
5. Diet. Don't eat refined carbs or any sugars. Focus on a high fat diet and only eat cars when you need to fuel before a hard session or race.
6. Up training distance gradually. Track things like resting heart rate at night or HRV to check whether you are over-doing it or not. Gut feel for this is probably more useful though. If you feel exhausted or you get pain then cut back on running and do more strength exercises.