Astrid I am like you. Do a little bit of alot but nothing complete. I always start with the washing machine also.
I do like the sound of doing one room at a time and to be honest I started this a few days ago. My normal routine is do abit of this then start something else so nothing every seems complete. Now of late my dining room I have spring cleaned completely (washed windows, skirting boards, walls completely sparkling clean) everyday or several times aday the kids trash it again but as underneath its clean all I need to do is pick up the toys, papers, quickly mop up some dirt from the shoes, pick up shoes etc. Now that underneath the room is so clean it only takes me 5mins if that (if I am not distracted) to have it completely tidy again.
Today I did the same to DD's bedroom. Its now sparkling. I know its only a matter of hours before she pulls clothes out, messes the bed etc but as its so clean it wont take much to make the bed again and tidy the things she messes up. So thats two rooms done (we have a big house)
Today I aim to do another room. The kitchen is gross (got flowers on the benches that need planting but its too hot) DH brief case and all these other things that dont have homes. Although the kitchen would be lovely to be clean as its such a high traffic area I find it impossible to clean it and keep it clean (its also old style so doesn't help and not very big) I am more concentrating on the living rooms and bedrooms and the kitchen will have to stay the way it is for now.
The office is a pigsty another high traffic area (3 computer hogs in this house) and no one sees it so it can stay that way for now.
Even with guests if you have one or two really tidy rooms you can shut the doors with any luck to bedrooms, laundry, office etc (if the kids remember to keep them shut) so you can sit in there with your guests. I find if you have a few clean rooms it looks better then having half clean rooms all over the house then a few clean and few messy (and with any luck you can close the doors so its not so noticeable) I am no housewife as I remind my husband but so far (in the week I have been doing it) I am finding it nice to have one tidy room. Now I just need to slowly work on a few more.