DON'T cook it- that sets the pectin which means you'll have to add pectinase to get rid of the pectin haze. Plus cooking fruit = cooked fruit flavor, not fresh fruit flavor.
Over the years I've added blueberries, raspberries, cranberries, cherries, peaches and apricots, usually to my light wheat ale. Here's what I do: Bought or picked, I freeze them, thaw and crush with a rolling pin (of course the stone fruits are destoned) then refreeze. The freeze/thaw/freeze cycle helps break down the cell walls. Then I add them to my 'secondary' and let sit for an additional week or two. Easy, and always works. I usually use about 1 lb. per gallon. No sanitation step necessary. After all, you're adding it to an acidic, alcoholic, low oxygen environment. Not much will grow in that.