What are the most important things you've learned in here?

What are the most important things you've learned from all the information on this forum? I'm in the process of writing my first novel-length book, and I know I don't have time to read everything. What are some highlights that I shouldn't miss? What are the general rules to stick to, and what are the most commonly made mistakes to avoid? What are tips you wish you had known before you started writing, that you would like to pass on? What are the best resources you've found? What are your insights? Please share!