I've tried varying my dose - putting it up if I've had a heavy evening meal of low GI foods which I know will keep producing sugar for many hours, but in the end I've found the guesstimates too inaccurate, so now adjust it about nor more than once a month after looking back at my readings. I'm now taking 4 units more a day than 2 years ago, so I don't vary it that much.
I find that varying my Novorapid (like Humalog) is, as expected, a much more responsive way of controlling sugars, but nothings perfect as I often get high morning readings and low afternoons.