Here are some methods I use:
-- Exercise is key. When you're physically in shape, it's easier to get the
motivation to exercise more and also easier to get the motivation to do
mental work and other stuff, I find.
-- Find fun and/or useful ways to exercise. I do learning activities (reading or singing)
during some types of exercise. Some of my exercise is to go places (walking, cycling).
Signing up for scheduled exercise classes can be a lot more motivating
than exercising alone at home.
-- Choose a simple, easy first step. One of the books (maybe by David Allen,
maybe somebody else) suggested changing into exercise clothes, because then
you start feeling like exercising. For other activities there may be other first
steps, like getting out a nice letter-opener; or standing up, walking around
in a circle, and saying "Now I'm going to ...". The tiny bit of exercise
increases blood flow and makes it easier to get the motivation. Saying something
out loud also helps.
-- Give yourself rewards. One of my problems is: I earn rewards but am too
busy to take them! So I usually try to choose rewards that don't take much time.
A reward can be a simple thing like looking at the pictures in a particular book.
If you've chosen it as a reward for a particular activity, then it will feel like a reward.
-- Positive reinforcement: one definition of this is pleasant things that happen
during (not after) the activity. For example, listening to music while doing something.
-- Divide the project into parts and plan a celebration after finishing each part.
Look at what you've done and feel good about that.
-- At the beginning of the day do something difficult you've been putting off; then do easier things the rest of the day. (see the book "Eat that Frog!".)
-- Set reasonable expectations for new habits: so your overall day will be somewhat
better than before, but not unrealistically totally changed. Once those new
habits are well ingrained, then you can move forward further to improve some more
habits. Trying to change too much at once may be too overwhelming. (according
to the book Willpower by Baumeister and Tierney.)
-- The Now Habit at Work by Fiore says to set a goal of doing new, good habits for
30 days. Preferably 30 consecutive days, but if you mess up one day, then you just
don't count that day, and continue counting from where you'd gotten to the day before. I really like this method! It's encouraging, not discouraging.
Inability is an abstract thing involving comparison with alternate universes; it cannot be experienced.