how many sets do you do per exercise?

Constantly mixing it up.

Last week my back was sort of out of wack so i did light weight work outs, but in the form of drop sets and high reps. My shoulders are still kind of hurting today.

 

Mix it up.

Ussually between 3 or 4 sets of 6-12 reps at challegning weight. Last rep should be very tough.

Some days I like to do 10 sets of 10 deadlifts and nothing else.

 

Agreed it is important to regularly mix it up to avoid ruts and plateaus.

You may find these two links interesting:

http://www.exrx.net/WeightTraining/LowVolumeTraining.html

http://www.exrx.net/WeightTraining/Guidelines.html

 

Depending on your age and the number of reps you do, I'd say 3 is more than enough for any one exercise. Hopefully, you are doing a few different exercises per muscle group, and as pointed out, muscle confusion is important (e.g., changing the routine to avoid plateaus).

 

I have. It’s an interesting way to i) shake up the routine and ii) efficiently do a full body workout in a relatively short period of time.

Takes some experimentation to find the right weight, but once you do, it’s worth trying for a month or so to see if you enjoy it and are happy with the results. Proper warm-up set and then a “work set” that truly goes to failure. It’s a different mind set but definitely worth trying.

Speaking of changing up the routine, another thing you may want to try is Strong Lifts 5x5. I did it for about 6 months and enjoyed it. Again, a different mind set and helps keep things fresh. http://stronglifts.com/

 

I did for two weeks last year. While I like challenging weight I found the very heavy weights I was dealing with with only six-eight reps a cause for concern. Especially squats.
I also broke a pair of sneakers and did the second week barefoot. In the end I decided it wasn't worth it.

 

It all depends on what your goals are. Many people are taught by trainers to do the same thing everyone else is doing. Resistive training for a specific sport is and should be different than trying to increase your overall health/appearance. Same goes for increasing endurance.

While formerly practicing physical therapy I would note many therapist rehabbing a UPS worker and having them to lift 50lbs ten times. The problem is that a UPS worker lifts many different types and weights of boxes for up to 10 hours/day not just 10 times and goes home. In this situation strength, endurance, and correct form are all equally important. When a muscle is fatigued there is a greater chance for injury.

I tell people who are looking for an overall program to increase some strength and change their appearance to do three sets of each exercise. They should do each set to fatigue but NOT stop at a certain number. They should count how many reps they are doing in each set but don't stop until they can no longer perform the exercise with the correct form. If on their third set they are doing more than 12 reps they should increase the weight increment by one level the next time they perform that exercise.

The other thing is to go slow. Too many people jerk weights around and end up with minimal results. I also encourage free weight use and as an example do a bicep curl while holding only one weight. This increases core stability/strength at the same time although the workout may take a little longer.

In addition, as others have posted, mix it up so the body does not adapt and you become bored.