If you want to write seriously you need to write every day.
This will require the following.
1) Setting aside time to use only for writing. Try to get a block of time rather than a few minutes here and there throughout the day.
2) Writing whether you feel inspired or not. If you think you're stuck on a current project then open a blank document and write something unrelated. The important thing is to get in the habit of writing for X amount of time every day.
3) Turning off or shutting out whatever might distract you. If it's the internet then disconnect your computer (or set up one with no internet connection). If it's the TV then shut it off or move it into a separate room. Same with cell-phones and video games. The time you set aside to write is for writing only. The rest can wait.
4) Being willing to sacrifice lazy habits. Setting aside time to write sometimes means getting up an hour earlier (or staying up an hour later). It may mean not spending as much time watching TV or surfing the web. Writing is more productive and (in the long run) more fulfilling than spending three hours watching TV shows you probably don't even like. Give up the non-productive in favor of the productive.
5) Sticking with it. Writing every day takes discipline. It may take a while to make it a permanent habit, but once you get in the habit you'll never have to complain about never having the time to write.