Habit. Set aside a time for practice and stick to it. Now that's easier said than done, but if you can get into a routine that you can stick with and which is recognized by all the others in your life, you will eliminate a lot of the excuses. It took me a couple of years to sort out the wife, kids, friends, job demands, etc. But now they all know that I'm serious about that time, and after almost a year, I find that that the excuses have kind of evaporated. I have a space carved out where the sax is always set up and ready to play, the music is on the stand, and the amp is set up to play backing tracks.
I'm an academic, and one of the things we have to do is write and publish lots of articles ("publish or perish"). I can come up with 10 excuses for not writing for every one you can come up with for not practicing. Back in the day, my Phd advisor asked me when during the day I wrote. I had no idea what he was talking about. Turns out he set aside time every morning to write, whether he had anything to write or not. He just did it because that's what he did. A couple of years ago I was talking with Larry Monroe from Berklee and I asked him if he still practiced (he's in his 70s). He said he practices the first two hours of every day, just to know that if he did not play any more that day at least he got his two hours in. Not because he loved to practice, but he said this is just what I do. I'm a musician. That was my inspiration to find that two hours.
So, when do you play?