Try to schedule a time to write and stick to it.
Stop criticizing your work it's probably not at bad as you think and everyone knows that first drafts are usually always awful, that's why they're first drafts.
Take writing seriously, not as just a hobby but if you want it to be your career then you have to FEEL like it is.
Take breaks, often! Especially if you've just finished something even if it is just a first draft or half of a first draft.
Setting deadlines can help as well, just don't be too hard on yourself if you fall short of them, try and do better next time.
Question your writer's block. What is slowing you down and suppressing your creativity? Are you just having a bad day or could it be more than that? Anxiety, depression? Explore your emotions and mind.
Work on more than one project at a time. If you're working on a novel and you're hitting dead ends, then remember your sense of humor and write a bunch of funny, quirky haikus or limericks. After all writing is suppose to be a joy.
Change the scenery, if you're always cooped up behind a desk all day then go outside on your deck or to the park or just change rooms.
Change your clothes, be comfortable.
Remember why you're writing and what your current project means to you. Don't give up.
Use writing prompts.
And probably most importantly...GET OFF THE INTERNET!!! Your friends on Facebook can wait and you can't post on your blog if you don't have anything written.