You should follow the Guy Kawasaki‘s rule 10/20/30 which means:
- 10 slides,
- 20 minutes to give your pitch, and
- 30 should be the smallest font size.
But, maybe even more important to remember is the top ten topics that venture capitalist care about:
- Business model
- Underlying magic/technology
- Marketing and sales
- Projections and milestones
- Status and time-line
- Summary and call to action
As far as number of slides is considered the rule of thumb could be one slide every two minutes. Bus some presenters use as many as four slides per minute. But there is a case when a little girl Sky McCloud confidently presented 200 slides in a 8-minute talk. So, good luck with your presentation!
Source: Duarte, Nancy: slide:ology. The Art and Science of Creating Great Presentations.