I took both subjects during my IGCSEs.
With Business Studies they can bombard you wwith questions from any chapter. In paper 1 go through the past papers and you'll notice the last sub question of each primary question tends to be repeated.
In paper 2 be well prepared with marketing, demand and supply, modes of communication and financial statements (this should be easy since you take accounting).
In accounting the format has changed so that there are MCQs on your first papers.
Profit and Loss accounts and Balance sheets are a favourite, so be well prepared with those.
Depreciation calculations and the theory regarding accounting conventions (prudence, historical cost etc.) should be concentrated on.