Starting Slow

Give your muscles (hypertrophy), bones (remodelling), ligaments, tendons, fascia and other soft tissues time to adapt to the increased load/demands/stimulus you are placing upon them (whatever it is you are doing). Keep in mind most of these different elements of your body will develop and adapt at different rates - tendons do so far more slowly than muscle, for instance.

This also gives you time to improve your technique and ensure you are using the full range of motion required. Not doing so makes you more likely to suffer injury, experience extended and increased soreness (such as DOMS) and increase recovery time.

Off putting, may make you give up.

Diet will help you both adapt and recover. As will sleep.

The UK NHS's Couch to 5k is a good example of starting slow.

Also see breathing, isometrics and mobility.