I do, what I think people call the snowball method or snowflake method or something like that.

I start with whatever scene I feel most passionate to write, could be a beginning scene or a middle scene or and end scene. Usually it's just one character (the MC) sitting somewhere and talking to someone (very Hills Like white Elephants style, because I write Literary Fantasy, so people sitting around and talking make up a good 90% of each on my novels).

So, I'll have the MC sitting by a campfire, resting after just putting up his tent and talking to his travel buddy, or I'll have the MC will be sitting at the bar talking to the bartender, or I'll have the MC in a busy marketplace arguing with a merchant over the price of some item... something like that.

Usually I have no clue how the conversation will go or what will happen next or how it'll connect to the main story, but I just start writing and see where it goes. The scene may not even make it to the final published novel either, because it's not important that I'm writing a scene I plan to publish, what's important is that I **JUST GET STARTED WRITING** and often I don't know where to start, so I'll sit there writing nothing.

As I'm writing I'll think things like: "What if random background character A, stole a spoon off the table, and the bartender yells stop thief, and the MC runs after the spoon thief, out into the street and nearly gets run over by a horse carriage, loses the thief, but is now sitting in the mud, while a stranger stops to see if he's hurt?" So, I'll write that into the scene and see where my mind takes it. A few minute later I'll think of another "What if..." scenario and write that and see where that goes.

It just keeps snowballing out, as I ask more "What ifs?" and add more random events. 

I think of this like going to the gym. Where you go to get your exercise done, but you can't just jump right into the heavy lifting, you have to first do your warm up stretches. I think of the main plot as the heavy lifting and these "What if" scenes as the warm up exercises I do to get ready to do the actual writing.

This method let's me jump right into the middle of a scene, always a dialogue between the MC and someone else, and let's me get into the writing zone, by free writing random shit that may or may not make the final cut.

The thing is, these scenes often do make it into the published end result, because often after 15 or 20 minutes of writing the MCs conversation, I'll be writing the MC get up and go off to do something else and the flow of one event to the next naturally leads to the primary plot and before I know it I'm in the full zone of writing the primary story.

So, I always start with the MC first (easy, I write a continuing series about 1 guy, Quaraun, and his 2 friends, BoomFuzzy and GhoulSpawn, so I already have the characters pre-made years ago and I know them very well after so many years of writing the series), and I drop him into the world (again easy because I built the world decades ago and already have a firm understand of it's logic, magic systems, government, etc, so I'm not world building anything, that's already done) and I just write him having a conversation and let the scene snowball from there adding "What if this happened?" as I write. 

It doesn't take me long before the random conversation leads to a random event which leads to another random event which leads to the primary plot and then BAM! I'm off writing the plot without even realizing I've started working on it.

Obviously I don't pre-plan or write outlines and I'm a full on pantser, and 2021 is my 43rd year writing this series, with the same MC in the same world using the same magic system, so I'm working with characters and world that are already fully fleshed out and don't need creating/building as I go. So, what I do, may not work for you if you lean towards making outlines or if you are still in the character creation and or world building or magic building stages. I think my method would probably only work for pantsers with ready to go characters and an already finished world.