When installing Windows 10 Technical Preview, you will not see an option to create a local account by default, and will instead have to log in to your Microsoft Account or be asked to create one.
You could create a local account after everything has been installed and you have logged in to your brand spanking new Windows 10 desktop (I tell you how, further down), but I found a better way.
The simple workaround? Just disable your Wifi or disconnect your network cable before installing Windows 10.
You will then get prompted to create a local account in the last stage of setup before you get to log in to the Windows 10 desktop. Easy peasy!
You already installed Windows 10 and want to switch from a Microsoft account to a local account? Read on!