There’s a difference between planning each step in a journey, and just knowing where you’re going next.
There are all types of writers, and no one can tell any other writer how to work their craft. All they can do is offer their best knowledge of what has been and may be successful, especially in terms of the process.
It’s easier to tell what a final product needs to succeed because there’s a measure for that; sales and reviews. What’s not so clear is what type of process will succeed, and options in that arena can only be judged by testimonials of other authors who have used them. (Some people sell theirs; up to you to decide which are worth the money, again by testimonials.)
So consider a spectrum when it comes to preparation: on one end is a writer who prepares each scene, conflict, arc, and effect before drafting, and on the other is someone with the vaguest of ideas (could be a situation, a single scene, or an image of a character) and off they go with a new sheet of paper and a pen.
For those who opt for less planning, consider what you’ve chosen to start with. You know the other elements will appear (or be created) as needed. The real technical work will come in revision/editing, so tracking what you’ve created already or that come to you for later use can make the process less painful later (or now, in the case of a stall/writers block).
Literal card collecting: Record each character on a card with what is known and any ideas for use again. Record locations that have been named or that may be revisited (and record possible uses). Note any themes that crop up and where, record ideas for future twists and turns (what-if or conflict cards, If you like). Collecting elements on physical cards, and ensuring you can navigate to the elements you need at will, provides a physical resource of material if the current line of thought fails. Yes, it’s a lot of writing, and it may not work for everyone. Programs are available for those who are more technologically inclined, like Scrivener or Ywriter.
Layering: This isn’t an original concept, but belongs to C.S. Lakin and is more fully outlined in her post Layers and Layers of Plot, Oh My. She goes into more depth, but the general gist is based in our experience of life. While there are main goals in a person’s life, for example a person might want to achieve world domination. This won’t happen right away, obviously, and there are other concerns for this character too. They might be in a financially unstable position (think Despicable Me and the Bank of Evil) which would have to be addressed either as a single conflict or an ongoing issue. Or there could be a love interest causing unnecessary and troubling “feelings” getting in the way of domination (Dr. Horrible’s Sing-Along Blog).
The technique is wonderful for pantsers, honestly, because with enough practice (or character development) a slow draft can be revived by shifting to another layer of concern within the story. Even without preparing these layers in advance, simply listing concerns in order of importance at the stalled scene produces avenues to explore. When layers of concern are addressed early on, there are more options for plot that can be revisited later (as long as you remember you started them). Keeping to two or three large, secondary concerns is often enough.
Excavate the story: In his book On Writing, Stephen King says, “Stories are found things, like fossils in the ground … Stories are relics, part of an undiscovered pre-existing world.” While this is just one man’s philosophy of writing, this perspective leads to a helpful approach for pantsers.
In rattling out a first draft on little more than a promising idea, there are several ways to “dig” out the rest. With the initial idea in mind, write down possible narrative avenues to pursue. This can be a character that comes to mind, a particular scene, or a question to be answered. Write the narrative in the direction of one of those discovered elements as long as there’s more to tell. If the direction doesn’t turn up good material, choose another that has potential to be interesting.
If an already-started draft is lagging, consider writing out the initial idea. Share this idea with people you trust and ask them to tell you what they would want to see. This should help uncover new ways to look at the story, or new ways to dig.