I always tried to treat the students with respect initially, then demand it in return.  The best way to discipline a middle school student is, to quote my husband, "play offense and not defense." 

The most important thing in dealing with middle school students it to work hard up front to build a positive relationship with them.  Once that is done discipline problems will decrease dramatically, but not disappear.  It is important to keep in mind that you should be a calm, non argumentative force and continue to treat a student with respect even as they misbehave.  Your anger will only fuel theirs, and calmness will win the day.  Talk to them quietly or bring them out into the hall to have a discussion with them.  This should solve a big percentage of your problems.

I certainly preferred teaching high school students to middle schoolers. Middle schoolers are still immature and can't really be treated as adults, unlike older high school students. I found that most middle schoolers were not ready to accept the responsibility of their own actions, and many tried to place the blame on other students or the teacher when they found their way into trouble--academic or disciplinary. Many middle schoolers were also quick to lie about things, and I found it harder to trust them than high schoolers. (I should point out that I taught middle school in a very poor area where few high school graduates went on to college. Many of the students came from broken, single-parent homes where drugs and alcohol played a major role in their upbringing, and where many of the parents had been dropouts themselves. Mistrust of teachers ran high among both students and parents.)

Whatever the age, discipline involves rules that must be followed through and not just "threatened". It is not good to say, "stop or you will get in trouble". This is an idle threat and not concrete. Kids need rules and boundaries--in fact, they crave them. So, have classroom rules displayed poster- sized and review the expectations you have. These can be norms for behavior, operations and expectations as to schoolwork. There should be clear- cut consequences. First time, talk to the student one-on-one. Next, a phone call home. Next, use the ladder of referral--it could be guidance, dean or social worker. But, be sure to stick to the rules and even if you appear to be "mean" and not their friend at first, that's okay. You are not their friend, but you are their role model and teacher.

I agree with both of the previous posters; I also have found that middle school students have a hard time trusting adults, so it's best to be honest with them, to always keep your promises (good or bad), and to never ever promise them something that you can't or won't make happen.

I use the "3 R's" - Have respect for yourself, respect for others, and respect for property. It's simple, and it covers every behavior you can think of.

The best way to discipline middle school students is to treat them respectfully.  Middle school is an awkward time, and students should usually be disciplined one on one.  There is a lot of posturing at this age, and if you try to discipline middle school students in front of other students, you are just going to escalate the situation.

This is the million dollar question in relation to middle school students as there is no one way as you know.  As a long time middle school teacher, I found that building a relationship with students was the key to discipline.  Discipline is never easy but becomes easier over time as you learn little tricks.  I loved teaching eighth graders who are the funniest creatures alive!  Discipline is easier if they know you really care about them, and that you will not tolerate behavior which gets in the way of learning.  I always made clear that we were in this learning together and then truly practiced that.  Stay aware of every little thing in the room as you can head off trouble that way.  Simply standing next to the one you suspect of throwing spitwads or pencils can end the behavior.  Starting the year with 3-4 important rules which you always enforce also helps.  I would remove a student until they could rejoin us when they had control of themselves.  Some I even took into the hall and watched walk up and down quickly to help them settle down.  I used squeezy balls to crush if they were blurting out and instantly removed them if they became a toy.  Keeping them all involved in lessons, with some lessons involving moving around the room using Kagan techniques helped also as too much sitting invites trouble.  I called parents early if there were problems or if there were positives to report.   I checked in with the social worker or counselor if there was one to find out what home was like. If I had tried all my methods with no success, I involved the office.  I also started each day fresh so that there were no holdover grudges from the day before.  I hope this helps because middle schoolers need teachers who truly enjoy them.