How to set/change the order of who signs

When you're setting up a document for someone to sign, whether from the "Sign Documents" tab or "Create Template" tab:

1. Click  the "+Signer" button to add signers to the document.
2. When you add signers, the "Assign signer order" option will appear with a tick box next to it.
3. Once you tick the "Assign signer order" box, you'll notice that up/down arrows appear to the left of the signer role.  
4. You can use those arrows to rearrange the order of signers.

When Signer 1 has signed the document, Signer 2 will be prompted via e-mail that it's his or her turn to sign, and so on.