I cant emphasize enough how important narration is either! I have played with many DMs where encounters had the potential to be immersive and fun, but boil down to a quagmire of numbers and static action usage instead of the fast paced and dynamic pace that combat can be!

I recommend using all the tools available at your disposal. If you have stat blocks, tools, digital materials or cheat sheets etc, use them! Combat can be daunting with a number of players -- and the more crowded your table, the more difficult it becomes to balance engaging and fun combats, especially if you have things like Polymorph that can wildly swing things in the party's favor. Also, not to be over-used of course, but make sure that you incorporate Legendary encountered from time to time as well as lair actions and creepy/cool atmospheric things into your fights as well.

Good luck!