suraya, There are a lot of things I want to answer at once, but I have to start somewhere. You are going to find I am putting the ball back in your court a bit, but what you're going to need to see is that I am trying to supply you with the answers you know better than I do. If you know how to fill in the blanks I start presenting and if have a good sense of judgment, then you're going to be able to find your way to the place you need to go, and I am just passing out maps.
First, this is a good opportunity, because not every company invests in the ideas of its employees when it comes to shaping job descriptions--or subject matter that needs to be looked at when assessing performance. You are obviously motivated about making good use of the opportunity and want to compare notes with other people--so I think you want this to be a good document.
Next, let's take a general route, and this is not much different form what Matt says in a way: what do you have to do this year, next year; what do you have to change or keep the same? What do you have to stop? And how does this get done by you or through the team that you are leading? Are any of those things already listed on the document you are calling your job description now? If no, then you can determine which ones need to be included and choose some wording for it.
Now here's a different way of looking at this: what do you want to do? (Emphasis on the WANT.) And I am talking about the position you are in at the company. Have there been times you thought of something but didn't bring it up for discussion? Are there rules that you don't want to break? Can you make new rules? Do you assess performance in the team? Do you look at certain things and grade them because that's the way it is (and do you want to put other things in the list and put certain ways lower in the list or OFF the list)? If you have been at this company a while and were in a different role before this Team Leader one, were you treated properly in every way? Can you treat someone better (not by being their friend, obviously, but by being an advocate for them, which means recognizing in a clear way what they are doing, and enabling them to see satisfaction in it? Do people do their work only because they must, or do they seem to choose to be happy through the work? There are lots of leadership questions packed into this paragraph, and I wonder if the answers you have for them, as someone who works at your company are one-word answers--or answers that make you think and look for the best one.
Look for the best answers for you too. Combine the "requirement" to do something that you should be recognized as having achieved (if/when you do achieve it) with options you "want" for yourself in this job description, so that you are choosing "happy" as well.
I've noticed in the last couple of years that I have been getting better at understanding the relationship between what people "want" and how you can put all of that next to "must"--at least where I work, but I have a lot of confidence that can be found in other places. And I think I have been learning that people do a lot better when they see that they have been able to choose something that will make them happy and incorporate that into their work, whether it's once in a while, often, or most of the time. And I don't mean extra break time and free food, I mean work that is motivating for a particular person with a particular brain and contribution of their own to make. You may not have a lot of room in your current role to make many, many changes that suit you (and that would cascade into your team and suit them), but you can explore and use the time between July 3, when you posted this, and July 15 to come up with what is going to make for a great revised job description that:
-gives you a new way of looking at what you are going to accomplish for your company, your department, your group of people, who work for you
-sets up a path for you and a path for the individuals in your team
-includes your personal input based on work you enjoy (and have not done enough of but can incorporate, as it is relevant)
So that it will be a document that you will look back upon next year and say, "Is that all?" | 
