Door signs are the first impression you give to parents and students before they enter your classroom. A beautiful, cheery sign will let them to know that you're happy they're there.
Bulletin boards are a great way to switch from season to season.
I've always found that rugs can make a huge difference in your classroom environment. When you invite students to come to floor, having a soft rug makes all the difference.
Wall decor can change the whole atmosphere of the classroom. When students can look around and see beautiful colors and inspiring messages, it'll create a positive learning environment.