You need to show 3 months bank statements.
Don't submit overdrawn statements. If it's totally unavoidable for some reason, then you will need to put good explanation why in writing.
I suggest you check out the application form and guide:-
Example of the form look here:-
http://www.ukba.homeoffice.gov.uk/si...etm0420091.pdf
Example of the ILR guidance look here:-
http://www.ukba.homeoffice.gov.uk/si...etm0420091.pdf