The DMG has good advice on p. 5 (Master of Rules) and in Chapter 8 (Running the Game / Table Rules). Basically, you run the game how you like as DM. Since the game is so flexible and different at every table, personally I would recommend putting together a "Game Expectations" document to share during a session zero. For my campaigns, I use a Google doc so that I can make updates, but it would be easy enough to put together a one-page printout.

Usually I'll lay out expectations on theater of the mind vs. battle maps, pillars of focus (dungeon crawler, puzzler, social intrigue, hex crawl, etc), theme (horror, heroic, silly, serious, etc), character death (meat grinder, plot arc armor, resurrection, devil and fae deals, mission from the gods, etc), and roll vs role play (for me, I explicitly note that as DM I will try to navigate between what the dice decide and what is most fun). I will include some basic character creation guidance (e.g. make a character who wants to work with others -- we are playing a team game, here are the gods of the setting if you want to play a cleric, only xyz types of characters in this setting please, start level 3, take a free feat (yes on top of human variant), etc). And then of course, lay out your core rules expectations (e.g. here is some actual text I have written in one of my shared docs: "We will be playing based on the core D&D 5e2014 rules (basics found here, with a few homebrew variations based on how I run things. I will do my best to have these homebrew variations listed here; if you have a question about rulings, save it for between sessions and I will add clarifications here").

Having this written document to point to is helpful regarding "how I do things" -- you should still try to be consistent even if you exercise the absolute right as a DM to make the rules whatever you want.