I soaked 2 oz of heavy toasted oak in just enough Jim Beam (Black I think) to cover it and soaked it for about 3 weeks while my stout was in primary. After primary I transferred to secondary for a week then added about half the oak chips for 2 weeks before bottling. If you don't primary you could probably add the chips just after fermentation ends. It added some nice oak-vanilla flavors, I think it worked out really nice.
I keep the remaining oak chips around and throw them in a commercial brew that I'm thinking of adding oak to, to see if I'd like to try a recipe in the future.