You’re probably familiar with the “butterfly effect” … the theory that if a butterfly flaps its wings in the Amazon, following the chain of reactions to that, there might be a tornado in Kansas three weeks later.
Part of the premise of D&D is that the actions the characters take should influence the world around them. Great in theory, but sometimes putting that into action can be difficult in practice.
So start small.
Think through the eyes of your main villain (or two or three if you have them).
They get news that the characters have done xyz thing.
What would they do? How would they react?
Start from there, and see where the rabbit hole … butterfly hole? … takes you.
The Road to Elturel: An Object Lesson in Adventure Design (Part 1) – The Angry GM
Project “Raptor” – Discover the unexplored Eberron! – Sage Advice
Anima Magic Items – DMsGuild – $1.00
Lansdon’s Marvellous Potions – DMsGuild – $1.00
Now get out there and tell a story!