As I may have mentioned, scenario analysis is really the integration of strategy and financial numbers. This means good news, and bad. The good news is that it is an appraisal technique that can be developed and implemented quite quickly. The bad news is that there is no formal module for learning it. It consists of a number of basic disciplines (Financial Accounting and Business Decision Analysis), and a good working knowledge of Excel. You can probably get good books on both of these at your local library, but there are none that really stand out.
Having said this, it is easier than it (now) sounds. Here are some guidelines about the technique:
1. Keep all of your assumptions on a separate page to the rest of your worksheets - this way they are explicit, and you can 'flex' them more easily.
2. Build each line of cost or revenue independently. The financial picture is like mother of pearl - layers and layers of thin detail.
3. When performing the 'what if' analyses, the art is in asking the right questions, which is where the strategic insight comes in.
As suggested here it is an art more than a science. However, if you have built the framework well, you can use brute force techniques to 'stress test' the financial projections. One of these is Monte-Carlo Simulation, which involves allowing all of the assumptions to move randomly within a range, and capturing the projections for, say 30,000 repetitions. This will tell you what catastrophic combinations could occur, and more importantly, how to avoid them.
If there is enough interest, I could put together a 'guru' piece on business modelling and scenario analysis. Let me know!