OK, so maybe not rocket science, but anyway, here goes:
Being a SAHM full time with dd1(4) and dd2(2.6) I have found that there is an amazing difference in how our days go - some seem to fly by, everyone is happy etc, whereas others we will all be grumpy and I will be counting the minutes till bed time. (The same went for weekends when I was a WOHM).
I have found that this makes a massive difference in turning most days into thoroughly pleasant ones:
When dd's wake up I greet them very positively and we cuddle a lot, tickle, laugh etc. Then they get to decide what to play for around an hour - I just go along with it and get involved in whatever they want to do. And then breakfast.
At this point dd's seem so content with having had attention (and food) that they happily continue playing while I shower and do stuff and they are in a much better mood for the rest of the day, regardless of what we choose to do.
So as I said, not rocket science, but a tip I would have found useful