To tone up...add weight or add reps?

I have a question for any weight trainers out there. I'm a woman and trying to tone up without bulking up...you know, long, lean muscles, isn't that what we all crave? So, I've been using the weight machines at the gym for some time now (I try for every other day, but usually ends up about twice a week maybe) and it's getting pretty easy/boring. So, my question is to challenge myself a little more and work toward achieving my goal, would it be best to add weight or add reps? I currently do 2 sets of 12. Thanks for any tips!

Its very hard for the most part for women to "bulk up" all that much. Women do not produce enough testoserone to be huge. I know a lady at the gym who lifts free weights at the gym, right along with most of the guys. You can not really tell she lifts weights but she is benching around 220lbs, which for the most part is pretty amazing.

If you wanted to maybe try free weights instead of the machines, anyone would get more benefit out of them than using machines. Dont get me wrong I still use machines but free weights are the main part of my workout. I would try sets like 12, 10, and 8, increasing the weight as you go. Being lean has more to do with your diet than anything, so eating healthy should be the main part of any workout plan.

Do more reps and go for three sets. You might want to do three sets of eight to begin with (no additional weight but a little variety to get you used to something new). On your next session, aim for three sets of ten and then three sets of twelve. If you really get into it then you have the choice of increasing reps to 15 or increasing sets to 4. This should help tone your muscles whilst adding strength without your muscles bulking up.

more reps

Well you can add weight and still gain nice lean muscle. And remember when you lift heavy you are improving on your strength. So do both, do a lot light weight rep training and do some heavier training once in a while. And to think by lifting more weights, you'll get bulkier is not true, if someone was trying to get bulkier it all depends on what you eat.