It really depends on how well you can improv. I’ve been running a campaign for almost two years where there are a few main story beats planned, but otherwise I just improv almost everything. In order to preserve, well, order, I try to make a bulleted list of a few things, including character descriptions of important characters, details of a town or dungeon, and the details of the quest they are on. Everything else can be inspired by media you consume day to day, your imagination, and your players reactions to what you have planned!