CIOs: If you're skilled at delegation, what made you good at it? For those who struggle, what methods have helped you improve?

Forget about micromanagement. Forget about technology management. You might be an expert in technical fields but now you have to work with and aggregate more people than technology. 

Create decision areas and establish decision makers on each area. 
Decision areas should be created as providers of services to other areas. I.e. support infrastructure provide services to datacenters who provide services to databases, middleware and applications a.s.o. This way each area will control the services they get.

Allow managers to make decisions and trust their decisions. Allow them to take risks and make mistakes.
Hint: Take their risk on you. As a CIO, it is supposed you understand their level of risk and make corrections when appropriate. Correction does not imply punishment. Punishment should be avoided. 
They will get the freedom to learn. They will get enough pressure from their peers and their service users.

They will get much more knowledge in their area than the one you may have. The ideal would be than each area decision manager would be better than you on that area. If they are not, give them time to learn.

Your technology knowledge is important for risk management and alignment both with business and inside IT organization. Not for detailed technical work.

This way the IT organization will be able to manage a much higher complexity, have better decisions and better services than without delegation.

I understand the strengths & weaknesses of each member of my team, as to identify their soft/hard skills too. With that in mind I can delegate easily and with confidence.

That is the result of the 1:1s I have with them on a weekly basis, the SCRUM cards I gave to them and the performance they have.

Delegation isn’t just a simple word, it is a follow-up process with robust communication ( Not micromanagement, only for those who required it ) that allows me understand where they are and for them, to know that I’m backing them up as their leader.