I am so fortunate to be a part of several writing groups, anthologies, and a critique group. The other writers are so supportive and willing to share what does and doesn't work for them. Here are the best pieces of advice that I've received over the years.
1. Keep writing. If you're marketing or querying a book, make sure that you're also working on your next book.
2. Don't give up. You're going to get a lot of feedback and negative comments. Make sure you learn what you can from the feedback. Then keep going. Don't let bad reviews paralyze you.
3. You can't expect to sell one hundred books at every signing. If you get to meet readers, booksellers, and librarians, then it was a good signing. Relationships and contacts are important too.
4. When you do appearances or signings, make sure you're well stocked with pens, bookmarks, giveaways, and candy. Always bring good candy. Chocolate is a hands-down favorite.
5. Know what your budget is for marketing your book and stick to it.
6. Use your new book to create interest in your earlier works.
7. Know what your budget is for conferences, memberships, and writing workshops. Work on your craft, but remember your primary job is to write your next book.
8. Social media and other marketing are key for authors. It's expected these days that the author has a key role in this. Just make sure that you balance this with your writing time.
9. Invest in your headshot/author photo. And make sure to update it as years pass.
10. If you're not able to create and maintain your website, invest in someone who can. You are your brand, and your graphics, website, business card, and marketing materials should look professional and branded.