Honestly your teachers will tell you to write as much as you can, thats sort of true it just depends how well you can write essays perhaps thats not your strength. 3 people in my class got band 5/6 for all our essays, we all had different styles. I tend not to keep writing and writing because your essay will often become contradictory, my demise of a small town essay was only 4 pages, hardly outstanding but it got the marks.
If you include maps (sketched) of your location, it always impresses...remember a scale...longitude and latitude.
Your opening paragraph should mention all your key points, don't worry if it's a bit long- if you run out of time at the end the marker can see what you would have said anyway.
hope that helps a bit
ps- Definitely mention stats of the town... population numbers...increasing or decreasing ect.
NEVER FORGET TO MENTION GLOBALISTION IN THIS TOPIC OR YOU'LL GET NO WHERE!