Fortunately, your Great Dane does not need a lot of grooming, at least not frequently, because there is a lot of real estate to cover! Great Danes are short and smooth-haired and usually only require brushing a few times a week and more thorough grooming every few weeks, to address ears, feet, and other soiled areas and to trim hair when and where necessary. If your Great Dane is a chill kind of fellow, this is no problem. If he is a little more high strung and energetic, calming your rather large friend before grooming may be necessary so you can adequately inspect all his nooks and crannies to remove dirt and extra hair and check for conditions that need to be addressed.
An excited or agitated Great Dane is going to be difficult to work with and calming him so he cooperates when you groom him is going to be necessary. Because let's face it, you probably can't outmuscle him like you can a Toy Poodle!