While having a conversation with a fellow fledgling writer, he mentioned he "didn't have time" to work on his current project. I mentioned that you make time for what's important in your life, so if you're not "making time" then it's not as important as other things.
This is, of course, true within reason. If you're exhausted after a long day of work, then even if you have time to write, it might not be a good idea to write--the words will probably feel as tired as you. There's also times when you're just not in the headspace to write--whether because the scene is dark and you're too happy or the scene is happy and you're too sad. But generally, if you make time to write, then you're going to write more than if you didn't make time. (Um, duh, right?)
He sheepishly agreed with me and said he deserved to hear that, since he applies that to so much else in his life/preaching. It's a good thing to apply to life. Obviously having kids (which he does) complicates things, since their priorities might not match with your own, but the logic still applies (just slightly tweaked).
I think of myself as fairly busy. I work full-time, ride horses at least twice a week, write and edit my own stuff, am (sorta) active in a writers' group, am a leader of a 4-H club, see my friends at least once a week, visit family (although not often enough), run my single-person household, and get 6-8 hours of sleep a night (which is mandatory for the happiness of the world). I've had people ask how I do it. Well, I follow some rules.
1. Schedule things. I joke with my mom, but I require most events to be scheduled at least a month in advance if you want my attendance. Anything less than that and I don't feel bad for saying "Sorry, busy!" Scheduling let's me know when I am going to have a busy weekend and need to reorganize other items. Say my Saturday is booked. Since my weekend mornings are prime writing time, then I need to either plan to write more on Sunday or else try to squeeze in more time during the week. Scheduling allows for optimal use of all of your time.
That said, don't overschedule to the point where you don't have any downtime built in. I tend to expect everything to take longer than it does, so I never feel rushed to do the next thing. I used to not be as good at that, and you burn out quick.
2. Prioritize. This gets back to what I was saying earlier. I used to (okay, we all know I still do) complain that I don't have time to write. And then I realized I couldn't write in the evenings after work because my head wasn't in the right spaces. But writing more was something I wanted to do. So I started setting aside time in some mornings to get up and write. Does it mean I sometimes roll out of bed when I'd rather be curled up browsing tumblr? Yes. But for me it's worth it.
Some mornings I may only write 200 words, but it's 200 more words than I had the night before. And just doing it feels like an accomplishment. And starting the morning with an accomplishment is a good way to do it!
Obviously this can apply to anything. But if you ever find yourself saying "I don't have time for X," but you spend your whole night watching reality TV shows, then you need to ask yourself, "Is reality TV more important than X to me?" If you keep spending your time that way, then yes, it is.
I'm lucky enough to have a fairly flexible schedule, and kids throw a wrench (or a whole toolbox) into working schedules, but if you really want to do the thing, then you have to make time to DO THE THING. If you come to the time to do the thing and you don't feel like it at that moment, then you can always do something else. But if you don't make the time to do the thing, then you'll never have time to do the thing.
3. Do the above to everything in your life. Now, I don't mean rank "friend time" vs "family time." But if you've seen your fiends a lot that week and you need some alone time, don't be afraid to say no if they invite you to a movie you're lukewarm on and you'd really rather be writing. Even if you can do thing X during when you'd usually slump on the couch watching TV, you might be able to do something else during that time, which would then open up a different slot for doing thing X.
And that's...pretty much it. I realize not everyone can/wants to have a life as structured as I do, but I think the core ideas can help everyone. No, you might not have a Google Calendar for every week sketching out when you have writing time, but having the idea of "I'll wake up twenty minutes earlier on Wednesdays to [do X] before I head to my job" is sometimes all we need.
Also, if you do all the above and find out you still "don't have time," then it just means that the thing you "want to do" isn't actually that important to you. And that's okay too. It might help to rephrase the thinking though: "I'd love to do X, but I have too many other awesome thing I'm busy doing." There's no shame in realizing that while something might be really cool and you'd like to do it, it just isn't that important in the grand scheme of things. As long as you're happy with the things you are making time for, then that's all that matters.