In the days of yesteryear (also known as the 80's and before) the internet wasn't really up and running. Any research for books was usually done with books, magazines, journals, and interviews. That was pretty good, but now we can take a fiction book and make it that much more AWESOME because of youtube.
Youtube.com is my go to for any sort of action/reaction of the human nature. It's also a huge source for abstract things...like the digestion system of a chicken. (Not joking, it's on there. Thank you people who put in on there for the good grade I'm going to get on my Poultry Production exam because of it)
Besides disecting chickens, you can also check out action scenes. Say you're writing a fighting scene, or a runaway scene. With normal research methods (including your own experience) you might come up with something like...
"Jared hopped from box to box, each one wobbling with his weight. In a dramatic jump, he launched over the barbed fence and into the junkyard. At the sound of barking dogs, he stood and began again."
Not that great. Check out this video though and see what you can add to the paragraph. (You don't have to watch the whole thing to get the gist.)
Pretty cool right? Most likely, if your character is really on the run, he isn't going to be showing off the like the guy in the movie, but you can see why some of the things he does can really help you character, especially if you're writing a distopian or apocalypse. (Also, if your characters are on the run, they might have to hunt. Finding "how to dress/skin animals" on youtube is a gruesome thing to watch, but it is helpful if you don't want to try it for yourself.)
With the new info you can rework your paragraph to something like...
"Jared launched off of the barrel. His back arched as he cruised over the barbed fence, it's metal teeth snapping at his shirt. The impact on the Earth vibrated up his body until his ears wiggled. The sound of barking dogs alerted him. The race wasn't over yet."Still, it could use some fine tuning, but you're in a better place than you were.
Going to youtube is also a great way to get an action or reaction that you don't have experience with or seeing something that doesn't happen often. Unlike the guy in the video above, I have no desire to jump off a building or run up a moving car. My characters might have to and that's where youtube enters the scene.
Maybe you're having a problem writing a scene because you don't have enough experience with what your character is doing. You can look it up all you want in books and articles, but there are some things, like the way your body moves when you're fighting with a sword, that you need to see someone do (or do yourself) to understand and therefore describe.
One note: Double check references and information. Sometimes the people talking are experts, other times they're not. It's still up to you to do the basic research.
Check out the videos below. Any great sentences coming to you? I'd love to hear them in the comments.