Spheres of totalitarian control:
1. Politics
It's quite obvious here, really. The Imperium's nobility are the only ruling class, with hereditary membership, of course.
2. Society
The Imperial society is atomized. The only unifying factor for its citizens is the Imperial Creed, and their workplace. First one is obviously desired as a means of indoctrination, the second one is a necessary evil and any guilds, syndicates or trade unions not in accord with the government(read not owned by the nobility)are eradicated on sight.
3. Culture
The Imperium controls its artists very strictly, only partially because of Slaanesh. All art needs to be sanctioned by appropriate Administratum officials, both its theme and style being evaluated. Desired purpose of art is propaganda,(strongly)suggested motifs are war and religion, as well as "slice of life" tales(of brave men doing their duties, of course). New horizons, beauty for its own sake and sex for purposes other than reproduction are a no-no.
4. Economy
Things an average citizen eats, drinks, sleeps in, wears, and so forth, basically everything in the market, is surplus from the supplies for war effort. A planet's industrial output, for example, will not be used to generate profit until the Black Ships are not filled with an amount of goods matching the requirements of tithe grade. Apart from that, it's pretty free-market(as much as you can get "free market" when it's the political elite who owns everything).
5. Private life
As said before, the aim is to make average Imperial human alone. Propaganda encourages distrust and paranoia, and the citizens are constantly on watch from the Arbites and the Inquisition, which they hold in absolute terror. Myriad regulations are enforced, regarding even the most basic aspects of human life, such as whom to marry, where will you spend your entire life, or what are you allowed to eat.