and start small. if you haven't been very active in a long time, your body will respond to minimal workout intensity.
i.e. do 1 warmup set, and 1 working set, per exercise. And stick to core moves like squats, deadlifts, pullups, bench press, military press, calf raises, and ab crunches/rev. crunches.
do that 6-8 weeks, then you can increase the volume and intensity a bit, as your body will have adapted somewhat to the increased physical activity.