I believe that the decorating your house are some of the best time spent with your family. I decorate my house for a number of reasons, mostly it would be birthday parties of family members. I totally love it.
I am currently living in a rental apartment. It can do with a coat of paint. I moved in a rush, therefore the landlord did not have a chance to renovate the premises. That said I rarely decorate because I do not entertain at home. My sister on the other hand knows how to decorate and keep house up to style.
It's very rare for me to decorate my place, like you mention it the only occasions when I do it are birthdays and Christmas, apart from that I have the same equal house all year long.
I never decorate my house, i'm living in a rental apartment so decorating is next to impossible...but as for cleaning, i do that generously like every other day...am what others say; a neat freak!
Me and my family doesn't decorate our house too much. We want it to be more simple and clean. Just a flower vase, 2 painting and some gundam or anime figures.
I decorate my house only once a year. The decoration is for Christmas only. Otherwise if it's about hanging some paintings on the walls, etc, that's always ongoing. I'm an amateur artist so when I create something which I think looks really good, it will end up on one of the walls of my living room.
I have only decorated one room in the past 3 years, although I'm planning on redecoration the dining room too pretty soon. A new carpet is all I really need and a new coat of paint, nothing drastic. The bathroom was done 4 years ago so nothing major needs to happen there.
If you are not including holidays, I would say that it does not really happen that often. Of course, my family goes all out on Christmas and other holidays like that, but other than that, we don't really do all that much.
Does your landlord let you do things with the paint and whatnot? I have known people who had apartments and they could not really do much as far as decorating went.
I stick to calm and cool colors in the house. Nothing to distract you mind or thoughts. Solid and bold furniture abound. Mostly manly style of decorating. Nothing feminine at all.