I feel like being a smart ass and just tell you to do pilates, but I'm going to resist.
It's actually rather hard to put on muscle - especially for women, so if you choose to do the low weight/high rep method, you'll probably just get bored to death and won't increase your muscle. To develop muscle tone, at the very least you should train in the 8-12 rep range, lifting weights heavy enough so your straining on those reps, not tossing them around. I can't tell you what weight to use - it's something you'll have to experiment with. The easiest way is to try a weight, say 15 lbs. on dumbell presses, and see how many reps you can do to failure. If you can do more than 12 reps, pick a higher weight and try again until you get to a weight you can only do 8-9 reps with. This would be your starting point. You'll probably gain strength fairly quickly if you're a newbie, which is why I'd advise starting in the 8 rep range. Within two workouts, I'd guess you'd be doing at least 10 reps or more with that same weight. Once you can do more than 10 reps with the weight, increase the weight.
This is a very basic method for a beginning weight lifter; it should help you develop muscle tone assuming your diet is somewhat in order. In other words, make sure you are eating ample protein. I don't know your stats, but try to get at least 0.8 grams of protein per lb. of bodyweight. Most of us intake 1-1.5 grams of protein per lb. of bodyweight, but at a minimum I'd shoot for 0.8.