It takes some strong organisational discipline to really maintain that throw away mindset - I suppose that's where it helps to make an explicit goal to throw the initial version away.

Another aspect is that (in my experience / opinion) if you're doing an MVP then it really needs to be as minimal as possible - big enough to give you evidence for your future plans but not comparable to what you eventually hope to build. Otherwise it's hard to adapt or to throw away.

The biggest thing I've found to help in any design work is making sure the engineers really understand the problem they're solving, so they can judge independently if plans they're making are complimentary to it.