For movies, Focus on the Family runs a website called Plugged In Online. I don't always agree with their ratings on "family friendliness" because they are incredibly conservative. But they are very detailed about what to expect in the movie in terms of language, sex, violence, etc.

As for books and tv shows, my mom always took an interest in what I was reading and watching. It was not unusual for her to come in and watch a few episodes of whatever series I was into at the time. With the books I got from the library, if she was unfamiliar with the author, she would wait until I set it down and read the summary on the back, or flat out ask me what the book was about. At that time, the internet was still developing, but there are a lot of resources out there now that were not available when I was growing up. You can try googling the book or the tv show to see what reviews are available about them, or you can also try reading the reviews on Netflix and Amazon.

I'm partially repeating info I posted in a previous question:

Here are some web sites that specialize in media reviews with respect to what's appropriate for kids:

• Common Sense Media
• Parent Reviews
• Kids in Mind

There are a variety of other ways you can find out about media (particularly movies) without having to see the whole film first. Here are some tips:

• Watch the trailer online -- this 2 minute investment can give you a pretty good idea if it will be scary, violent, or sexy (because those movies want to make it very clear from the trailers that it contains such things, to get people to see it).
• Use IMDB to look up the film and see what other work the director and writers have done -- maybe they are things you've seen and liked (or not), and you can read the comments and reviews about those previous movies from the same creators.
• Look in a newspaper (or its web site) -- major papers almost always have reviews when a movie opens that not only discuss the film in detail, but also generally point out which bits might be an issue for kids.
• There are TV shows that review movies, for example in the US there is a popular show "At The Movies" (a long time ago, it was hosted by Siskel and Ebert, but now it's a different set of reviewers). You don't have to agree with their reviews, but just listening to them talk about movies for a couple minutes can give you a good idea about what to expect from each one.
• You may disagree with MPAA ratings (I think they are too permissive with violence and gore, too restrictive with fairly tame nudity and sexuality), but they are relatively consistent. Considering a PG-13 movie? It'll probably have a bunch of people die and more swear words than you expect from a kid's movie. Don't be surprised, it's meant for teenagers.

Finally, resist the temptation to see things the weekend they open. By the second week, the "buzz" will be well established about what the films really are (not just the pre-release messaging the marketers wanted you to hear) and you can make a better judgment. Maybe even somebody else you know has seen it and can tell you about it.