Start with the smallest form of the habit you want to create. It should be so tiny as to be achievable when you are at your least motivated and most fatigued. Attach it to another, appropriate, behaviour which is already an engrained part of your day; brushing your teeth, going to the toilet, eating lunch, etc.
For example, if you wanted to read more have a book on your phone and every time you sit on the toilet read a sentence or two (or three).
Do not track failure. If one day you find yourself on Twitter instead don’t worry about it, move on.
Do reward yourself. Not with anything big, but just say “I’m awesome”, or pump the air with your fist. If it feels silly all the better, it should make you smile. It works.

With your newly adopted tiny habit you can maybe try expanding it. If you’re in a queue, take out your phone and read a few more sentences of that book. If you’re at home looking for something to do while you eat breakfast, read the book!
Now you’re reading a book a month. That’s 12 good books a year! Certainly better than zero.

Tiny habits - make the change you can actually make. Start from where you are not at where you want to be.

For much more on this read BJ Fogg’s brilliant book.