It seems when writers start out they feel as though they must write the perfect sentence, followed by another perfect sentence, that in turn will lead to a valuable plot point while carefully crafting your book's world along the way.
It doesn't work like that.
Often your first draft is simply you telling yourself the story. Don't be surprised when you reread it to yourself if you still don't understand everything you were trying to say. Use the parts that are golden and rewrite the rest. Make it so you understand it, then when you understand it, go back through a third and maybe even a fourth time to make sure your sentences are clean. That the narrative stands on its own as a whole. Then and only then will your drafts be ready for other eyes. Don't make that mistake of sending a first draft to someone. It may feel amazing to complete your first work but you will only make their eyes roll into the back of their head as they pick apart what you meant to say.
For example, when I finished my first draft of my first novel it came in at roughly 84,000 words. In the rewrite I must have rewritten 60-70% of the entire book and now it is only about 76,000 words. Was it scary to delete all that material? Hell yes. I deleted nearly 19,000 words and several useless MacGuffins in one day. For safety's sake I copied and pasted those extra words into another document even though I know that in a few month's time I will delete all those extra pieces. It's all right though, it made editing that day much easier.
Now that I've rewritten the first manuscript I'm letting it rest and have returned to the second manuscript. Even though I had the first chapter written in the second manuscript I deleted it in its entirety when I came back. It's okay to not like what you wrote the first time, it isn't okay to give up on your writing. The world needs your ideas.