Although some teachers start with just a classroom welcome letter, I personally recommend to begin the school year by preparing a whole written informational packet about your classroom and teaching philosophy. Include contact information, web page, and best time to reach you. For an added bonus, have the informational packet available on your classroom web page. The informational packet that I prepare (and update each year) is several pages long and includes welcome information for: meet the teacher page, class schedule, behavioral policy, homework policy, classroom rules and a detailed summary of each curriculum area and my expectations for academic success.
Give a detailed description of each content area and what your expectations are for the child at home and at school in the content area. For example, when telling the parents about the reading curriculum, include the name of the reading program and the phonics program that the school utilizes. Also, include a list or detailed description of the curriculum, including your expectations for learning in word work (for example, how many sight words are the students accountable to know at the end of the school year?). Do this for each content area.
Parents will appreciate that you told them what your expectations are. At the end of one school year, I had parents come to me, packet in hand, delighted that I wrote that their Kindergartener would read independently at the end of the school year and that indeed she was reading independently.
If you are forthcoming about your expectations with the parents, then they can set goals for the child at home and reinforce what you are doing in the classroom. I have even had parents adapt my classroom behavior and award policy at home to help keep consistent expectations between school and home. The informational packet can become quite lengthy, but the rewards it delivers will be worth the time that it takes to prepare it.
During the school year, keep parents informed of which unit of study you are in for each content area by weekly or monthly newsletters. In each newsletter, give them ideas on how to reinforce the subject matter at home.