Suppose that you need to write something: a manual of cake-baking, a novel, or a Ph.D. dissertion. Are you despairing that you can't keep at it, day by day, week by week, month by month?
Here is what to do.
Take a small piece of blank paper: 4" x 6" or smaller. Keep this piece of paper on your desk, right near your elbow.
Each day if you manage to accomplish something--anything--on your project, write it down on the piece of paper. Examples:
"Signed four books out of the library."
"Read fifteen pages of Lloyd's book and took notes."
"Wrote to the cake museum in Dusseldorf."
"Wrote three pages."
"Revised seven pages."
"Sent draft of Chapter 3 to my thesis supervisor."
Now the important part: each day, when you have written down your wonderful accomplishments, draw a little smiley face on your piece of paper. Colour it with a yellow highlighter or coloured pencil. Well done!
As you fill these pieces of paper you will see that you have made progress. The work done on a single day may seem tiny, but it all adds up. When you fill a page, file it in the place where you keep your treasured mementos (mine is called "Letters and Souvenirs") and start a new page.
I followed this method to complete my Ph.D. and I have told some of my colleagues about it. May it help you also. Good luck!