Open the Migration Assistant program on your iMac and the Mac mini. It should be in the "Other" folder in the Finder Applications folder or in Launchpad. It will walk you through the steps of transferring your data. It should do it wirelessly, but you might need a cable.
Here's a photo of what the program looks like (It's the one in the red box).
[image|2972643]
Let us know how it goes!