According to the website applications open on the 2nd febuary, and we should be able to apply online this year, or so I heard. (all going well)
If you want to apply as a group, and all live in a house/flat together then you will be better off going to the accommodation office and picking up a paper form id have thought as you have to give the candidate numbers and other details of those you want to live with.
If possible, all go along together and fill in the forms there and then. Try and give in your forms asap as a few of my friends didnt get their first choice last year (who applied as a group) when reapplying for halls as they applied just before the deadline date.