This is a key question. The general answer is:

1. For realistic cases, there is no such theorem, and so the task of choosing a good system is a lot about choosing one which doesn't reward strategy in realistic cases.

2. Roughly speaking, my educated intuition is that strategic payoffs grow insofar as you know that the distinctions you care about are orthogonal to what the average/modal/median voter cares about. So insofar as you are average/modal/median, your strategic incentive should be low; which is a way of saying that a good voting system can have low strategy for most voters in most elections.

2a. It may be possible to make this intuition rigorous, and prove that no system can make strategy non-viable for the orthogonal-preferenced voter. However, that would involve a lot of statistics and random variables.... I guess that's what I'm learning in my PhD so eventually I may be up to taking on this proof.

1. The exception, the realistic case where there are a number of voters who have an interest that's orthogonal to the average voter, is a case called the chicken dilemma, which I'll talk about a lot more in section 6. Chicken strategy is by far the trickiest realistic strategy to design away.