Does scry happen before or after you draw in effects that say 'scry then draw'?

When a spell or ability says 'scry N, then draw a card,' you perform the scry first, then draw. The golden rule of sequencing is that instructions on a card are followed in the order they appear (CR 609.3). This is not optional — you cannot choose to draw first.

Scry lets you look at the top N cards of your library and arrange them (moving any to the bottom in any order, CR 701.18). Because you scry before drawing, you get to decide whether to keep the top card on top or send it to the bottom — and then you draw whatever card ends up on top as a result of that scry.

This ordering is very intentional game design: it means the draw is 'improved' by the scry, since you already filtered what's sitting on top of your library before the draw happens.

Example: You cast Opt (scry 1, then draw a card). You look at the top card — it's a land you don't need. You put it on the bottom. Now you draw, getting the card that was second from the top. The scry's filtering directly benefited your draw.

Note: if an effect said 'draw a card, then scry' (rare, but hypothetically), you would draw first. Always follow written order (CR 609.3).