I've not grown many potatoes before, and they were years ago, so this will be a bit of an experiment. I've used Ruby Lou seed potatoes, mainly because I couldn't find any Royal Blue. Everything you read tells you to use seed potatoes, rather than ones from the shops, so you don't bring disease into the garden. I'm not sure how risky this is but best not take a chance.
I've planted them in a trench about 30cm deep which I will gradually fill up around the plants as they grow. About 80% of the crop grows above the original seed apparently, so this trench will end up as a mound.