It depends on your goals. if you want to work in German academia, then it's not a great option. I think there are lots of great books on writing good research proposals, but high acceptance is about whether your school has a potential supervisor who is working on your topic or in your theoretical framework. If you don't already have supervisors identified, then I don't really see the point in applying to any excellent business school.

thanks Duncan!
i want to work in Asia,
Source of Good research proposal? i will work on any topic.@Duncan you are HHL alumni,plz guide .

If you want to work in Asia as an academic, then take your PhD at a school with a higher profile in Asia. if you don't want to be an academic, don't take a PhD. If you don't know what you want to research, take a masters in research for a year and refine your proposal in the context of a business school with a strong research setting. Look for something like http://www.business-school.ed.ac.uk/msc/msc-by-research

For tips on writing a proposal, then see https://www.google.co.uk/webhp?sourceid=chrome-instant&ion=1&espv=2&ie=UTF-8#q=how%20to%20write%20a%20phd%20research%20proposal