Set expressions are all about selections (or searches). Can you manually apply a selection that includes the data you are looking for? If the answer is YES, then the set expression usually is fairly easy to compose.
For more advanced set analysis you might need to look at using set operators to find the data area where your results should come from. P() and E() functions can also be handy to target possible and excluded results in advance set analysis.
The Help or reference manual cover the possibilities in the Set Analysis chapter.
To get an accurate answer to your specific questions I think you need to provide a sample QVW, so that your data can be evaluate and put in context of the expression.