For a moment, think about your classroom. What messages does it send to your students? Is it bright? Cheery? My third classroom didn't have any windows, so there was never any sunshine. I made sure I put up a couple of bright bulletin boards, and some nice pictures, just so it wouldn't matter to students.
Now, you may be thinking, "She's just going to tell me to decorate my room! I'm not necessarily creative.". Not really. I do think our rooms need to be jazzed up, but that's different for first grade and for high school. However, no matter what grade you teach, there are some key things to consider.
First, do you have something posted that tells students they can be successful? You might think just telling them is enough, but it's important to post quotes about success--and you'll find some starters in the column to the right. You can put them all together, or scatter them around the room--one year, I even posted them on the ceiling.
Next, consider putting up posters of successful people. These can be famous role models, or have your students create their own posters. Ask them to put their name, something unique about themselves, one thing they are proud of that they have done, and one thing they want to learn this year. Then post those as reminders of their achievements and goals.
Finally, how will you celebrate learning? One year, I put up a blank bulletin board with a note: "What We're Proud Of" at the top. Each two weeks, students would post something they had done that they were proud of (of course, remove the grades for privacy). It's a great way to focus on students' progress, and to encourage students to self-reflect. You can keep some cutouts of sunshines if they would prefer to write something, rather than post work.
Regardless of what you do, enjoy your year! If you are happy about what you are doing, your students will be more likely to enjoy your class, which will ultimately increase learning.