Starting out, I did aerobics (elliptical) 3x/week and strength training 2x/week.
For strength training, there are several good books available. Two of my favorites are "Body For Life" and "Weight Training For Dummies". Both have lots of pictures & lots of advice. I've seen the recommendation that you should not train the same body part within 48 hours. If you do a whole body workout, then just take at least a day off between sessions. Or, you can do legs one day and arms the next.
You probably should also train your core -- abs and back muscles. Some ways to do this include crunches, ab machines, pilates, yoga, etc...
For aerobics, it's recommended that you train at 65-80% of your heart rate at least 20 minutes. You should also warm up and cool down. I usually just hit the "cool down" button on whatever cardio machine I'm using.
Finally, you should stretch after you're warmed up (for instance, at the end of your workout).
I recommend trying to do at least one session with a trainer so that you can make sure you're doing your weight lifting properly. Sometimes they have strength training classes you can do also.
Good luck & I hope this helps
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