Off the top of my head, I'd go 1.5-2lbs beef, 1lb spuds, 3 carrots and 1 onion. But I do like my meat! Beef cube in water is fine, prob between 300-500ml. Make sure the spuds and veg are under liquid if poss, and around the same sized chunks for each type of veg. Brown the meat before chucking it in if you like.
If you're doing dumplings they take about 30 mins, but switch it to high setting beforehand and try to keep them out the liquid as much as poss.
Chuck in bay leaf/herbs/seasoning etc as you like. I think it's recommended to put dried herbs in towards the end of cooking.
Enjoy!