There are always lessons from a year of school.
First and foremost, you can't be nice enough. It's always right to be kind, and when challenged with regard to kindness, that can be difficult. Teaching throws you all kinds curves, and as much as possible, catch those curve balls with kindness.
Reserve Judgement. It can be tempting to make judgements quickly when you first meet students, families, and colleagues, but you'll almost always regret making judgements hastily. Instead keep a notebook of anecdotes, notes, scores, and other factors to support the judgements you make later--judgements related to all kinds of student services and progress reports.
Collaborate. Particularly when issues are tough, you don't want to go it alone. You need to work as a team with regard to tough issues. Seek the consult of colleagues, family members, administrators and students. Take the time you need to think it out and make a good response, decision, or plan.
Take the Job Seriously. Every part of the job matters so treat it that way. Bring a professional attitude, speak, and effort to teaching and learning every day.
Have a Sense of Humor. Be prepared to laugh at yourself and enjoy a laugh with others. That's critical, yet never have a laugh at a child's expense.
When Aggravated Remove Yourself From the Situation. You'll never do wrong to take a break. It's the best thing to do when aggravation, frustration, or confusion hits. Time and space works wonders.
Connect with other invested educators and continue to update and renew your knowledge and service--this will keep you fresh and develop your practice in ways that matter.
I'm sure I'll add to this list in the days to come.