1) Excel and Financial modeling - the best course I know is Training The Street. Take Financial Modeling, Valuation, Maybe LBO. They have the amazing templates that you have to repsoduce to be able to do that fast.
The key thing - throw away your mouse and put some tape on your touchpad. Do everything with your keyboard!
2) Power Point
- First, read "Say it with charts" and "Pyramid Principle".
- As a next step Google for MBB presentations on SlideShare and try to replicate them in PPT.
- Finally, take MBA some cases (HBS or any other) and try to derive the conclusions and put them on slides using MBB styles.
And finally - take a long vacation before starting your job;)