Write your heart out.
The first sentence can be written only after the last sentence has been written. FIRST DRAFTS ARE HELL. FINAL DRAFTS, PARADISE.
You are writing for your contemporaries — not for Posterity. If you are lucky, your contemporaries will become Posterity.
Here are just 3 of the tips on writing from Joyce Carol Oates over at Brain Pickings. You know you want to read the other 7.