DM Tips- Improv: How to prep for it and manage things when the players go on a tangent

I started playing D&D in 1980 with the Holmes Basic Set. I didn't know any other players so I was forced to devise a way to play solo. The next year, I met a group of AD&D players in search of a DM. Impatient to start playing, I convinced them to let me do it, even though I had never seen a group play before. I assumed that I was required to fully play every NPC including supplying voices and mannerisms. My players were surprised at first but gradually we grew to really love this way of playing. For me, it started a lifelong love of tabletop roleplaying. Being a DM released a flood of creativity that might've otherwise remained dormant. I might never have been curious about a career in the arts if it wasn't for my early experiences playing D&D and other role playing games. Eventually, this led to a 30 year career as an actor, musician, composer, writer, and director working in the fields of music, theater, film, and television. (If you're at all curious, my largest part to date was playing a main character on Season 4 of The Sinner on USA Network / Netflix). In the 90s, I wrote a module for Shadowrun 2e - Paradise Lost, published by FASA, and also contributed to the Denver Box Set. I still love playing them - D&D and Shadowrun are my two most commonly played systems but I have enjoyed a number of different RPGs including GURPS, Flashing Blades, Boot Hill and Tunnels and Trolls.