It's exciting to start working out. Short-term goals are obvious. Easy to get into a 'push past the pain/I DESERVE this pain/10 more minutes and my a$$ will be that much smaller' masochism. Especially if you've worked out before. Easy, therefore, to get injury.
Spasms, sprains, bad knees & ankles - I've had them all this way! My advice: even if you're returning, start at a beginner's level. Don't start with a 5 day workout plan: 2 or 3 days a week is fine! Take it easy!
Listen to pain - and stop even before you feel it, as a beginner. That INCLUDES the initial soreness (DOMS) you feel the first few days after a workout. Don't do it again until that's gone. Walk instead!
Accept where you're at.
No crazy plans until you're at a reasonable level of fitness.