I've got a work permit here and I'm thinking of taking a brief holiday overseas. What do I need to do so that the work permit does not expire immediately upon my return?

Your work permit is not the issue, your visas is - Make sure you get a reentry visa before you leave.

If you holiday is over the period of your work permit renewal, go on different dates

Your work permit is not the issue, your visas is - Make sure you get a reentry visa before you leave.

If you holiday is over the period of your work permit renewal, go on different dates

Thanks. I imagine I just go to any immigration office and fill out the relevant forms?

Yes and you can get single Re-entry visas or miltiple re-entry visas which would save you going back again.