In this day and age, however, I think the problem is not so much "writer's block" as it is distractions, distractions, and more distractions. You know what I'm talking about: YouTube, Facebook, TV, texting, phones... It's so much easier (and sometimes more fun) to scroll through Facebook and see what funny memes have been posted, or who's in a relationship with who. Worst of all is when you start off watching a video on YouTube and fifty clicks later realize that you've just lost an hour or so watching cute cats, music videos, or the videos you can't unsee but wish you could. Imagine how much you could have written in that hour!
If there's one universal cure for distractions it would be self-discipline (at least the ones in which you're distracting yourself-- can't help ya with the noisy kids/neighbors/pets or other real life things). Turn off your phone/internet if you have to. Make it less accessible so that you're less likely to mindlessly go to Facebook when halfway through a paragraph. More than anything, though, when you find that you can't seem to focus on what it is you want to write, for whatever reason, there's a trick that's help me to wade through the writer's block, distractions, and sometimes lack of inspiration. I conditioned myself.
To be more technical about it, I turned myself into my own psychological experiment by using conditioning to produce the ability to write. Lately, I haven't had writer's block per se, rather than an inability to focus on one idea long enough to get anything done. During the semester I had almost no time to myself to write my fiction, so instead ideas began to pile up. After finals, I had so many things I wanted to write that I kept bouncing between them until I ended up with nothing but a wet tissue as I sobbed in the bathtub for my consistent failure. I felt a little like Sisyphus (the guy who was doomed to roll a rock up a hill just for it to roll back down before reaching the top for all eternity).
For the sake of simplicity, and less words (because who wants to read so many words?) I'll try to put the idea into a list, using my own personal methods, since I'm sure everyone will have their own.
1. Have a specific story or even just a character in mind that you wish to write about. Making it one or two characters helps to narrow down the focus immensely, since every story has one or two characters that are at the heart of it. This worked very well for my mad scientist protagonist in my book The Brethren Souls, Augustus Fargeau, who was rather specific in my mind from the moment I thought him up.
2. Find something that did or continues to inspire you for this story/characters. This can be music, a book, a video, pictures-- wherever you find your muse. Heck, it could even be food. Make popcorn, or some other deliciously smelly snack where the fragrance can work as a trigger. In my experience, music is the best muse. I have playlists up the wahzoo for characters and stories where songs (with lyrics or instrumental) instantly get me in the mood and sometimes mindframe of a character. Everytime I hear the song, I think of the character and it gets my brain juices flowing. For Fargeau, there was one song in particular that worked for both the character and the story as a whole thanks to the atmosphere and the lyrics created by a band called Professor Fate. The song is "Limbo" if you're curious:
3. Find a way to associate that muse with your writing. Music makes this easier, I think, because you can listen to it while typing away madly. I've done this to the point that I can't listen to certain songs without my fingers twitching over an invisible keyboard and a character's voice intruding on my thoughts. (Non-writers might think that sounds unhealthy, but it's really not, I swear.)
4. One way to take it a step further is to make sure you have a good writing place. You've probably heard it before that you need a good workspace, and it's true. If it's messy or uncomfortable, you're not going to get jack-squat done.
5. Yet another step further is to find a specific time of day to do your writing, if possible. Schedules can be crazy, I know, but all it takes is the hour before you go to bed, or maybe an hour before you go to work/school. Or, if you're like me, your brain functions best at a specific time of the day no matter what you do. Against my preference, my creativity activates between midnight and 8 am. The hours that I should be sleeping. Which sucks. A lot. But at least I know my "writing cycle," as it were.
There are probably other tricks that could be used, but this is the best one I know at the moment. The best way to utilize it is for it to be done repeatedly until it has an effect (hence "conditioning").