Bangers and mash is quick and easy to make; the main thing you need to look out for are good sausages, meaning a high meat content. The minimum meat content of a pork sausage is only 42%. The equivalent figures for most other sausages are around 30%. These figures are low but they are the legal minimum and most producers will use more meat.
Everyone has their own way of cooking sausages and making mash. I rather like coarse sausages and I like to fry them slowly to brown them all over.
My gravy contains onions fried with pancetta until all is soft, then I add fresh beef stock or vegetable stock and season it. I like to use some dried thyme, some wholegrain mustard, a little bit of marmite, freshly ground salt and pepper and some brown sugar. I cook the gravy on a high heat with no lid to reduce it and to get even more flavour.
For my mashed potatoes I use slightly overcooked mealy potatoes and use a ricer rather than a masher as the mash will turn out even smoother that way. Once all your potatoes are mashed add some hot milk, a knob of butter, some salt and freshly ground nutmeg. Whisk rigorously until you got rid of all lumps!