* * *
In short, visit as many different houses as you can, and take a tour. Maybe it's your friend's house or apartment. Look for open houses you'll never be able to afford, and at open houses in places your character might live. (Be honest and tell the Realtor you are just looking, and not planning on buying within the year, so they don't waste time on you). I worked as a maid for a short time in LA, long ago, and got to see the insides of some incredible homes.
For cities/towns: go to as many places as you can, different cities, or even look online at Google Maps, or watch movies set in cities you want to write about.
I mainly use my own experiences if I'm going to draw on realism for little bits here and there, rather than family history. However, my family history affects who I am, and what sort of experiences I've had.
My family is very New York, (Brooklyn on my dad's side, Manhattan on my mom's), and very Jewish. Having been raised in a Jewish home, it absolutely affects my writing, even if I don't mention religion at all (and even if I consider myself to be a Jewish Christian, now). Someone once pointed out that it's pretty hard to find someone eating pork in my books, lol! I have never in my life eaten a pork chop, or even know how to prepare one, so it wouldn't feel "real" to me to add a small detail like that.
I often use settings I know well, which is why you'll find a lot of stories set where I grew up, in the expensive suburb of NYC that is Westchester County, NY. (Think The Enslaved Trilogy, set in Westchester, NY and NYC, or The Tycoon's Convenient Bride...and Baby, also set in Westchester), and in cities I spent time living in, like NYC (The Pulse Trilogy) and Los Angeles (Hollywood Spank). I'm currently living in northern Idaho, and I'm writing a cowboy romance set in... north Idaho! :)
The careers my heroes and heroines have are almost always those that I've done myself (I've been an RN, EMT, housekeeper, telemarketer, actress, video store clerk, you name it!) -- or a career I know about from a friend, or one of my parents' friends, in addition to whatever research I add on top of it. My parents have some long-time family friends with incredible jobs in NY, and that's where I fashion the careers of most of my Tycoons and Billionaires (sadly, I don't personally know any actual billionaires). There are more than a couple of nurses in my books, since I worked as an RN before leaving to write full time.
As I mentioned above, a long time before that, I worked as a housekeeper for rich folks in LA. I was very, very bad at this job, and didn't last long, lol. But I got an indepth look at amazing houses, at the nooks and crannies and closets and luxurious bathrooms, and I use those settings for my heroes' homes. However, long chunks of description are boring -- when I describe the layout of a house, it's usually only done as it relates to the character, such as "She peered over the open balcony looking down into the great room, watching him as he sat reading before the roaring fire."
I like to know what the interior house already looks like in my head, so I always use a real life point of reference, whether it's a tiny cabin in the woods, a suburban home, or a castle.
Many homes I write are dressed up versions of houses I know well, simply for the layout. I need to know in my head exactly where the kitchen is, where the heroine will head for the door and what room she'll end up in -- and it has to be the same, throughout the book. Some authors even draw a "blueprint" to stay on track!
If on page 1, your character can hear what's being said in the kitchen while she's in the living room, then she'll have to remember to whisper if she says something in the living room that she doesn't want people in the kitchen to know on page 96.
If on page 3, she stares out the window of the bedroom and sees the people walking by the front sidewalk, then she can't forget to close the blinds on page 82 when she undresses and needs privacy.
That's it! I'll repeat here what I put at the top, to close this up, because otherwise I'll just keep thinking of examples. Little details pulled from real-life homes, cities, and jobs that you already know well, can add that extra depth and realism to your fiction.