congratulations!
is it for a quota place or for the open competition?
if the former, read the guidelines carefully and make sure you have satisfactorily answered all the required stuff.
if the latter, do talk to your prospective supervisor, they should help you. also, look up the ESRC's current focus areas. Is there any way you can weave them into your project? do also consider how your research might generate "useful" stuff for a wider audience, that could get you all-important extra points.