Well, yes, this is the thing, and for something quite simple they do take a bit of practice. They should feel quite soft. They will be rubbery if you add lots of flour. They should feel nice and light in your hands. Don't add milk to the mash, just a bit of butter. I still don't make them as well as my mum. Will make them again soon, and try to come up with a good analogy for how they should feel.