Same as JNieman.
All pre-release dwgs (submittals, internal changes) are alphabetical.
Initial IFC set is Rev 0.
Any subsequent changes are designated numerically.
"Depending on the clients requirements"
That is a frightening statement, I know.
Generally we do the same as JNieman and hermanm.
... with the following modification.
We consider that a document 'revision' is not just for "Public Issue" documents. A system should allow us to identify revisions and status when the document is still in-house.
For In-House 'revisions' we use the notation W<x> where x is an incrementing number. The 'W' indicates 'Working-In-Progress'
So the document before public issue can be saved/archived and rev'd at any stage. This is handy for recording progress claims, identifying the state of a document prior to design changes, or just identifying the status regarding progress ie: detailed, in checking, in back-drafting, 'delayed' for client information etc etc.
Public issue either 'For Review' or 'For Construction'
Documents for review will have Alpha revision id's (A originally), incrementing for subsequent review issues.
Documents for construction will have numeric revision id's (0 originally), incrementing for subsequent issues.
Any internal changes to a previously issued document shall have the W<x> internal identifier appended to the public revision id. EG : if a rev 'A' document is reworked internally the revision is changed to AW1, AW2 etc for internal identification prior to it's next public issue.
This may sound like a bit of work but the identifiable demonstrable control is comforting, and sometimes critical.
Some people tend to forget that drawings are legal documents and need to be identifiable.
Each document can be archived with the revision id appended to the document number at any stage of its progress or at each milestone event.
Of course, this process is made effortless by having software to control it.
... particularly if the system changes from client to client or project to project.
ps. and the answer to the next question is 'A Dollar A Day'