I recently created a runtime demo of an existing solution. A couple of things need to be done:
1) sample data: the solution needs suitable non-confidential and copyright-free data to display the features of the system and allow users to get started immediately.
2) consider functional differences between normal client and the runtime engine: the most striking difference is the disabled close box on all windows, which prevents them from being closed, but also consider the lack of pdf creation and charting.
3) time or functionality restrictions: code might need to be added to prevent full functionality, say to 30 days or whatever.
4) installer program to assist the users in getting the solution onto their computer, particularly for the Windows operating system.
Once these are sorted -- and they require some thought -- the actual creation of the runtime is relatively trivial.
If you decide that you don't need sample data, time or functionality restrictions or an installer program, you'll still need to take into account the functional differences of the runtime. With my solution I use print preview windows as part of the printing functionality, and it quickly became obvious that these are a problem because the user has no way to close them! So to get the runtime working nicely, the print steps might need to be changed to not display the preview in a separate window for the runtime.