my biggest suggestion (as someone who has really bad focus problems I mean seriously I should be working right now.) is to discipline yourself, because lets face it:
you wont be able to do anything if you aren't able to actually sit down and do it. wishing wont work! try small steps towards working for longer and more consecutive periods of time.
try working on an hour(be it writing, thumbnailing, staring at the page) then up the time a little more each time or w.e. for me, I like to create soundtracks of music that makes me think of the story and I listen to those on a loop to keep me INTO the story. (I also demand that no one bother me while im working) since you can easily be pulled out.
try doodling first, and it may be hard, but always try to doodle something relevant to a story your working on, even if they aren't the greatest idea, you gotta work through crap ones to get gold.
also if you get restless, get up and walk around your house/apt, or excersize a little.
even if you need to take many breaks, as long as your getting back in there and working you should feel proud.
also , although in the face of everything stated above, make sure you WANT to work at that time (or on that story) because otherwise the work will suffer if your hearts not into it. so if its not a good day, then just chill that day. but don't get in the habit of using that as a get out of jail free card for not working!
okay ive said too much, GOOD LUCK1!!