It happens to all writers: it’s time to write and either A) you don’t feel like it, or B) you don’t know what to write. Each is a distinct problem with different solutions, but often the new writer treats them as the same thing with statements like: “not feeling it” or “muse didn’t show up today”.
More experienced writers know that if we always waited for the muse to show up we never would get anything done—fickle creature that muse is. Often nowhere to be found when it’s actually time to write, and constantly whispering in your ear when it’s impossible to write, such as in the middle of a business meeting. So the easy solution to A) is BIC, Butt In Chair. Regardless of how you feel, you make the commitment to face the blank page on a regular scheduled basis. The result of this is some sessions are spectacular, others abysmal, but always forward progress is made, even if it’s a baby step. The result at the end of the day is the reader can’t tell the difference between those sessions (with some editing and smoothing of course—I’m not really a huge proponent of large-scale edits, but that’s another post).
The solution to B) is equally as simple, just write the next sentence. Take it one sentence at a time. What really helps with this approach is to recognize and accept that not everything you write is gold or even has to be used. You’re absolutely allowed to write crap to get warmed up—just cut it out or come back to it. Another good trick that I like, is to write the previous scene from another POV. Granted this a lot of work that will never appear in the story, but it will give you deeper insight into the scene which may unlock for you where to go next. However, the most sensible thing to do is to end your last writing session in the middle of a scene where you know where to go from there.
Writer’s block happens to all of us, but having strategies in place beforehand renders this malady impotent.