Many people, especially women, avoid weight training because somewhere along the way they heard that it will make their muscles big. This is simply a matter of misinformation. Strength training is a critical element to create muscle tone and burn fat and should not be left out of your well rounded routine.
Every pound of muscle you have burns ~ 30-50 calories more in a day. The more lean mass you have, the more calories you burn. Without some kind of weight or resistance training, you're likely to reach a plateau quickly and you won't achieve those nicely sculpted muscles.
Light to moderate weights with between 12-20 repetitions are most
effective for toning lean muscle mass. Building large muscles takes a
great deal of discipline and a very strict regimen of heavier weights.
Body builders work for years to get the muscle mass that they exhibit.
Stick to the moderate weights, enough to challenge your muscles at
the higher reps and your muscles will be sleek and toned without any
bulk. If you're still not sure, hire a personal trainer to help you decide what workout will help to reach your health goals.