I made a list of the key aspects in my life. Then chose the most important. On balance, I chose 'food'. This is vital for my survival, and is easier to modify than 'sleep' or 'hydration' or other single-variable aspects. Food is really, really important both in terms of immediate benefit and its contribution to my longer term goals.
So: 'food'; where does it come from? Well, supermarkets usually, though there are other options to list as well, but we'll start with supermarkets in Phase 1, and consider internet deliveries, growing my own, etc as part of Phase 2. There are five supermarkets nearby, each with differing benefits of cost, convenience, proximity, quality of goods, range of goods, and service.
I produced a weighted scoring matrix as recommended, and I then developed an action plan to optimise my food choices, but the benefits really aren't as major as I'd hoped.
Er.... no. Really, NO. This may be flippant, but the point is really serious: 'importance' really isn't that important. Important things tend to pretty much take care of themselves, without too much conscious effort.
Similarly, urgent things tend to push themselves to the front of the queue anyway, and the benefits of categorising tasks on the basis of urgent, not-urgent, important, not-important, tend to be overstated. It is much more productive too root out the unimportant aspects of our lives, and to do things in a sensible sequence (which might not always mean urgent things first).