I've been thinking a lot about worldbuilding recently. My husband and I are working through one of our favorite TV shows, Stargate SG-1, and we both keep commenting on how rich the world of the show seems.
Since my husband is a writer too, we inevitably started to analyze exactly what it was the writers were doing to make the show so interesting. We eventually broke it down to one main point.
This show is absolutely crammed with details. Because it's sci-fi, the protagonists are going to other planets and encountering other races and cultures. The writers sprinkle in little differences between those societies and our own (which may be as simple as an oddly shaped drinking glass, or a quick hand gesture when greeting a friend).
When I think over recent books I really enjoyed, I realize that they are all rich in detail. This doesn't just apply to sci-fi, either. I just finished a Regency romance that I couldn't put down, mostly because it included tidbits of everyday life during the time period, things I'd never read in other books. Part of the reason contemporary novels like Eleanor and Park resonate with readers is because the author includes the details of the characters' lives--the clothes they wear, the music they listen to, the way they react to things around them.
One great thing about including lots of details is that the technique helps avoid the dreaded infodump.
This happens when writers try to give a load of backstory very quickly and can be very off-putting for readers. Sprinkling details into your narrative is a much better way to hint at the differences between our world and the world of the story.
For example, instead of coming out and saying there was a great war between our hero's nation and the neighboring one, why not have a character looking at someone's war medal? Or maybe show the wreckage of a building that was destroyed by enemy troops?
Of course, anything can be overdone. For an interesting discussion of what happens when you overdo it on the details, check out this blog post by author Kate Elliot on the Tor.com blog: The Status Quo Does Not Need World Building.