Reading AND writing are vital for anyone who wants to be a writer. There are so many reasons to support reading that I won’t bother going into it—I am sure you can make your own list.
However . . . reading while early in your writing process might be a bad idea.
Why? Because you don’t want what you are currently reading to shape what you are writing.
Ever since I became serious about writing, I pick apart every novel I read: examining how the author achieves whatever he/she creates. I look at how much description is there, where it shows up, the use of imagery and figurative language, the dialogue, how we learn about the characters, how the setting, tone, and point of view are established, etc. These are all excellent things to analyze and will give you (as a writer) plenty to consider.
But if you are doing this as you write, you will be tempted to follow the cues of the book you happen to be reading. This might be subliminal but it can just as easily be the thought, “he/she did __ well and I bet I could do something similar in my own book when ___.”
Particularly in the early writing stages as you put your story together and map it out, you must guard yourself against outside influences. Reading and/or talking to someone about your story will result in stifling your creativity. There will be time for discussion and revision—but if you want to create something new, you must listen to your own muse and no one else’s.