Every time I brainstorm or critique or give feedback to someone on a creative work of theirs, I always find myself asking,
What’s your point?
In other words: what are you trying to say; what do you want to explore; why do you want to tell this story; why do we want to listen?
This has the same significance whether it’s a one-panel comic or an epic novel series. There can be, and usually is, a difference between the plot (“what happens”) and the point/moral (“what it’s about”). There are a number of ways to tell the same story, and a number of reasons that story could be told. Some reasons are noble, some are indulgent, and none of it really matters. As long as you have that reason for telling your story, you have direction. It’s like having a customer/user/persona when you’re developing a product: you have a focus, a goal. All decisions made in the telling of a story, or the creation of a product, are answered by comparing whether it will help achieve the goal, whether it is in line with the focus.
When you feel that a scene or line is weak, when you start playing around with the storyline, come back and ask yourself, “What’s my point? What’s the point of this scene?” If it doesn’t advance the plot or the characters towards the goal, try changing it to something that does.