Weight training is a great way to tone up, boost your metabolism, help burn fat, and prevent injury. It's good to focus on your whole body and large muscle groups. This will make you stronger the fastest. It's very easy to do, and you don't need a lot of equipment. To learn more, go to the link above. You might want to get a good book with illustrations since there are a million different exercises to choose from. Or do a session with a trainer, or use the machines at the gym. However, with just a few free weights or a resistance band at home, you can do all the weight training you need in your own bedroom in front of the t.v. How awesome is that? I also love my exercise ball. I can do all sorts of core (abs) exercises on it as well as lots of other things. They're pretty cheap and easy to keep in the house.
To get started, I recommend 30-45 minutes 2 to 3 times a week with 24-48 hours of rest in between sessions. Focus on the entire body. Shoot for 2-3 sets of 10 repetitions for each set. By the end of 10 reps, your muscles should be very fatigued. It should take almost everything you got to push out that last rep. Rest for 30 seconds to a minute between reps.
Always maintain good form (back straight, abs contracted). If you're really straining, lighten the weight. If it's too easy, increase the weight. Experiment until you find what's right. You may have to play with the weight or the type of exercise you're doing. Every body responds differently. Stop if you have any sharp pain. You may be sore the next morning, and that's good. It means it's working!
Below, I've listed my favorite exercises for all major parts of the body. There are countless exercises so experiment and find the ones that work for you. Good luck!
My overall favorites:
1. Push-up: mostly chest, some triceps
2. Bench press: chest
3. Pull-ups: back, biceps; everything for me; the all-time hardest
4. Lat pull-down or rows: lats, back
5. Shoulder raises: shoulders (push weights up over head)
6. Triceps extensions: triceps (backs of arms)
7. Bicep curls: biceps (fronts of arms)
8. For Abs there are a million: crunches on ball and bicycles are my favorites
9. Dead-lifts: lower back; hamstrings (backs of legs); some glutes
10. Squats: glutes; quads (fronts of legs)
11. Lunges: glutes; quads
I want to be brief so as not to overwhelm anyone. I'm not going into a lot of detail on each exercise b/c illustrations are best. Refer to the link for more ideas, and please, ask me questions to clarify anything. Hope this is helpful!