For the first day of school don’t stress too much about getting everything perfect. Decorate some but it will come together as the year progresses. Just make sure you have a welcoming environment for the students to walk into. One major thing to think about is where and how you want your student desks arranged. I’ve observed that most teachers, including myself, arrange their desks in some sort of groups. Don’t make your groups too big as it may encourage chatting! I would recommend groups of 4. Also keep in mind things that may distract the students such as windows and doors. According to Back to School Teacher Tips the Keys to Good Classroom Design are:

• Ensure an easy flow of traffic throughout the room and keep high traffic areas, such as those near the teacher’s desk, pencil sharpener, and wastebasket, free from congestion.
• Make sure you have a clear view of all students at all times
• Ensure that students can easily see instructional displays and presentations.
• Make storage space and materials readily accessible.

I agree with these tips BUT realistically its hard to stick to all of these depending on your room size and shape. Just keep them in mind as your plan your room design.