I have learned this:
When dh is not doing what is expected, let's say it is to sign a tax form that needs his signature, I must say, "Here is the 2015 personal tax form. Sign here please." Look him in the eye and hand him a pen and the form.
I don't say, "The tax form is on the kitchen counter, will you sign them please so they can get in the mail?"
I don't say, "When will you sign the tax forms? They have been on the counter for 5 days."
I don't say, "Let's do the taxes together. What day would you be available to that with me?"
I don't say, "It's your turn to do the taxes."
I don't say, "Do you think you will be able to sign the tax forms today?"
I say, "Here is the tax form. Sign here." hand him the pen and the form. Then stand there and wait until he writes down his name. It's up to me to be firm and not accept any excuses or diversions from him.