Can't speak to a pressure cooker, but we had crockpot roast last night.
Cut slits in the meat and insert whole garlic cloves. Rub all over with mustard powder, rosemary, and salt/pepper.
No matter the method, cook until done! :)
Why would you want to pressure cook meat!?! It will ruin it. We wish to cook meat at as low a temperature as safely possible, never as high as possible.
The whole purpose of pressure cookers is to allow higher temperatures than are possible at 1 atmosphere. They artificially increase the pressure, which allows higher temperatures to be obtained (see Ideal Gas Law). They are used for canning because botulism bacteria must be cooked hotter than 100 deg C, the boiling pt of water, to completely kill them. Unless you are canning the meat, there's no reason to pressure cook.
Not sure about brisket, but I've done short ribs in a pressure cooker. Frankly, I'll never do them again any other way. I've done roasts in a pressure cooker as well. That works out great as well. Since brisket is pretty tough, a pressure cooker is a great idea for brisket. I would salt & pepper it, sear it in some (coconut!) oil in the pressure cooker, add some onions, garlic, red wine, broth, and you should be on your way. I would go with a 30 minute cook after it comes to pressure.
I cook all kinds of meats in the pressure cooker, so it's for more than canning. Living at an elevation of 6000 feet, it takes forever to cook on the stove. I find that it tenderizes the meat and infuses flavor in it while shortening the cooking time.
Like Ed said, sear it in Coconut oil and then make some sort of a rub of your favorite seasonings... salt, pepper, garlic, savory, etc. Experiment a little. If you want to really break it down and shred it, then cook it for an hour.