A practical guide for Malachain readers, written from everyday experience.
The mistake almost everyone makes is to run the way they used to. After a long break the heart and lungs recover quickly but tendons and joints take months, so the plan has to be slower than feels necessary. Alternate one minute of easy running with ninety seconds of walking, three times a week, and add a little running each week.
Run slowly enough to hold a conversation, replace shoes that are more than a year old, and take a rest day between runs. Niggles that disappear after a warm-up are normal; pain that changes how you run is a sign to stop and walk home. In about nine weeks most people can run for thirty minutes without stopping, which is the point where running starts to feel like a reward.
It also helps to talk the subject through with friends or colleagues who have tried something similar. Their experience points out the details that guides leave out: how long things really take, which costs were unexpected, and which shortcuts turned out to be a mistake.
There is more to learn on this subject, and the linked website goes into greater depth. Treat this article as an introduction rather than the final word, and check any important decision against up-to-date, reliable sources before relying on it.
If you try any of these ideas, start small and adjust them to your own situation. What works for one person will not suit everyone, and it is fine to keep only the parts that help. Writing down what you changed, and what happened, makes it much easier to see after a few weeks whether the effort was worthwhile.