I am trying to overcome this as well. For me, my excuses are extremely pathetic. Like today I have to be somewhere at 11:00 and I'm heading out of town tomorrow AM. I have a list of things I HAVE to do/take care of before I leave.

I look at my list and think to myself 'I don't have time to do all that before I leave, so I won't do any of it.'

Here are some things I do:

Tell myself that I will do X for only 5 minutes. After the timer dings, I can keep going or quit.

Ask myself 'why not do X now?' What is stopping me from doing X now? Is there a reason?

Look at how much time I have to do something. Like right now, I have about an hour before I need to leave. What on my to-do list could I take care of in less than an hour? I have a few tasks that would take about 15-30 minutes each. I can't do all of them, but I can scratch off one or two.

Write tasks on index cards, with a time estimate. Sort cards in the order I want to complete tasks and hold one card at a time (to help with focus).

I have a few more ideas and comments about nebulous stuff, like losing weight, but I need to kick myself off the computer. So much good advice posted above - breaking stuff down into small chunks really helps.