• Start light. As a beginner, you must start with light weights. It may be only 1 or 2.5 lbs - whatever works for you.
• Build up. When performing 12 repetitions of the same motion (that's called one "set" of 12 "reps") becomes too easy, then it's time to add weight.
• Work each muscle group. Work each muscle group (arms, shoulders, abdomen, chest, back and legs) with only one or two sets.
• Warm up. Don't forget to warm up beforehand with five to ten minutes of stretching or light aerobic activity like walking.
• Take regular breaks. A good routine only takes 20-30 minutes a few times a week. In fact, resting between weight-training workouts is essential in order to allow your muscles time to recover.

Of course, you'll also want to ensure you're using correct form so read up on the subject, rent a DVD or, if you have a gym membership, ask a trainer.