With APC's, people generally size down 2-3 sizes. I am a 30 waist, and have a pair of New Cures in a 26 waist (I know, they stretched massively) and a pair of Petit Standards in a 27. Both give me a lovely slim/skinny fit (the PS are definitely the skinnier of the two).
I am no expert in how the New Standards fit, but I would try and size down by at least two as they are a fair amount wider than the aforementioned.
I have read of people sizing down by 4+ with the New Standards to achieve a slim/skinny fit, which seems ridiculous to me when APC offer slimmer alternatives, but there you go.
BSB's advice is spot on.
If you get the jeans and the legs fit, but the waist is too tight just wear them around and slowly start to button the jeans up. When I got both pairs of mine I could barely do the top button up, and now both fit me perfectly (it probably took a god 30-60 minutes of wear around the house before I could button them up to the top). The jeans are as tight as a virgin at first, but they get a lot comfier after 3 weeks of good wear.
(PS: I love APC, but I wouldn't call myself an expert, though I'm flattered with the title )