When using a thematic unit:
Identify what goals and learning standards and objectives you need to address.
What considerations about your student's needs will you need to address.
Select at topic (usually one that students will find engaging and meaningful to them))
Brainstorm ideas on how to use this theme for each subject.
Create and schedule when you will use this theme during the day and or week.
Plan for small-group, one on one and large group activities.
Plan for accomodations for all students
How will you assess what the children are learning?
Arrange the environment (how do you want it set up?)
Remember to think about your goals and objectives but think about the learning interests of your students also :)
Plan a thematic unit and use it! I used one every single week that I taught. Does it take a lot of planning? YES, but it is so worth it.