There are many do's and don'ts.
1. The first and biggest that causes most problems for patients is using heat on a fresh injury. Use ICE first. Wrap an ice bag in a damp cloth and put on the lower back for 10 minutes tops. Give the area a 30 minute break and reapply.
Remember the first injury brings inflammation, the ICE helps to remove that. And yes it doesn't feel as good as heat but works vastly better.
2. Just because the pain eases quickly does not mean the problems is gone. Wait several days to allow the area to heal.
3. Just because you feel pain in the leg, groin or even knee does not mean that the problem cannot come from the lower back area.