I've never yet experienced Writer's Block. I suppose it will happen to me someday, but so far, no. Occasionally I get stuck on whether I want to do something or not, but not for long. The best advice I can give to people who frequently get stuck is to have multiple projects going. Sometimes I find it's not flowing on one project, but the door opens right away for me on another one. Sometimes I have to write something technical when what I really want to do is write something sexy or dramatic. Or I have to write a lemon scene, but I'm not in the mood and want to nail down plot details for a future scene or story instead. If I don't feel like writing, but I have to because I have some sort of deadline, then I just power through and do it anyway.
I find writing to be about 50 percent joy and 50 percent chore. I only do it because I think people are going to enjoy my writing the way I have enjoyed reading other people's books and fanfics. I am not doing it for myself. I don't need to do it for myself. My head is full of movies and I can enjoy them anytime without going to all the trouble of converting them into the written word, a process which takes many, many hours.
Finding the time to write is a big challenge. I work, I have family obligations, and I have a lot of friends. My husband and I love to entertain. We have parties and we go to parties. Plus, there are all my girlfriends that I like to meet one on one for various activities. I used to steal writing time from the hours when I should have been sleeping, but I managed to really trash my health by doing that over the course of about three years, so I don't do it anymore. Even if I have insomnia, I don't get up and write. I needed to make a clean break from my habit of writing all night. I don't recommend that anyone choose writing over sleep. Or exercise. Writing must be part of a balanced life.
In particularly busy weeks, I give up on writing altogether. In general, however, I am alert for opportunities to write. For example, if it's a weekend and my husband lies down for a nap, I have a choice. I can either lie down with him, or grab half an hour of writing time. Sometimes I choose the nap! Or if it's a weeknight, I hurry through my workout at the gym so that I can come home and get twenty minutes of writing time before I have to start getting dinner on. Sometimes that twenty minutes gets eaten up by family, though. My family members tend to show up when they know I will be home, predictable creature of habit that I am. Sometimes I opt not to answer the phone, even if it's a dear friend calling. If I answer the phone, the call will take 30 to 45 minutes, which means good-bye to my tiny hoard of writing time. I choose not to watch TV most of the time because TV can make the limited hours of the evening disappear and then there is nothing to show for it at the end. My evenings are really short anyway, because I exercise after work, and then I cook dinner when I get home from the gym. As a writer, I am acutely conscious of time. What time is it now, how many hours are left in the evening, will I be able to create a piece of time for myself at any point today or tomorrow? Time is precious to me because I have so little of it. It's far more important than money. I wish I could change this in my life. I sometimes have fantasies about running away to a remote location where there are no other people. I believe I would get a lot of writing done, but perhaps I'm wrong. The old adage "If you want something done, ask a busy man" has some truth to it, I think. Busy people get more done than people who have all the time in the world. When I sit down at my computer knowing that I have only half an hour to produce something, it probably sharpens my focus.
Some people are able to write during quiet times at work, but I find there are too many interruptions there. Also, because I'm in work mode, I can't really get into writing mode. Another obstacle is that I'm frequently interrupted because I work in a place where clients can drop in.
I usually take my morning coffee/dinner to the computer and write sentences between sips or bites of food.
Whenever I approach the end of a project, I usually experience a slowdown. Part of this is practical. Wrapping up the end of a chapter or the end of a story means more re-reading of what I have already written, just to make sure I'm accounting for the loose ends, and also, to pick up the threads of where I left off. Sometimes all the re-reading to pick up the threads takes all of my available time and then I have to go to work or cook dinner or fulfill social obligations without having been able to get to the writing part. Another part of it is psychological, but this doesn't happen at the end of chapters, only at the end of long stories. I slow down a lot. It's almost like I don't want to say goodbye. Or maybe a fear of letting go. I'm not sure why it happens. I'm only guessing.
I don't focus on trying to achieve a set number of words per day. That doesn't work for me. When I have time, I can produce five to seven thousand words in a day. When I'm too busy to get near my computer, of course my word count is going to be zero, sometimes for days on end.
I think that being a productive writer is about being conscious of time and how you to choose to spend it. At least, that's what works for me.