The best exercise to get a toned back is the pull up and it is probably the exercise that most women avoid.
The pull up is such an amazing exercise as it incorporates various muscle groups and as a result gives you that toned muscular back that you can't achieve with other exercises.
A few months back I couldn't do any pull ups as I just thought it was something I would never be strong enough to do. My boyfriend was constantly encouraging me to try it and used to assist me by lifting me up, but as we don't work out together I wasn't doing them enough to get good at them.
After a bit of research I decided to invest in a rubberbanditz assisted pull up band. There are various different types of bands which you choose based on your weight and the amount of unassisted pull ups you can do. The easier the bands become you should be moving on to the next band.The pull up band assists you when doing pull ups so you don't need someone to spot you.
At the beginning I could only do a few reps but now a few months on I can do a good amount of reps with the bands and have started doing reps without the bands as well as I have built up the strength. The most important thing is to create good form and I think the bands allow you to do this. They never get easy but it is addictive when you see the results it gives you.
A bonus is that it also works your core!
There are many different assistance levels and you must choose based on your weight and the amount of reps you can do.