Out of all the agent blogs out there (and there are plenty of them, big and small), probably the biggest blog is Nathan Bransford's. He is an agent with Curtis Brown out in San Francisco, and his blog is uber-popular and always worth reading.
Recently, Nathan did a "Positivity Week" that was great, and there was one post I thought I'd share. It's called the "10 Commandments for the Happy Writer." See the full post on his blog to enjoy the long version; check out the short version below.
1. Enjoy the present
2. Maintain your integrity
3. Recognize the forces that are outside of your control
4. Don’t neglect your friends and family
5. Don't Quit Your Day Job
6. Keep up with publishing industry news.
7. Reach out to fellow writers
8. Park your jealousy at the door
9. Be thankful for what you have
10. Keep writing