Dear Varsha,
Here are a few tips for you; I hope they will help:
1. You can choose themes based on the month. For example, December could be related to winter, July to summer, and if it's a festive month, make the theme according to the festival.
2. Ensure that each month offers something new, different from the previous month's theme. Selecting a single theme for the whole year could become monotonous. Therefore, having different themes each month will make it more lively.
3. You can choose one theme for each month and repeat it every year. Alternatively, you can make random selections. Hence, all you need to do is decide on a total of 12 themes and repeat them each year or make it a random selection.
4. For November, consider the special days falling in this month. Based on that, organize an event. For example, on the 14th, which is Children's Day, you can encourage your employees to donate something (other than money) to a charity organization or orphanage to help improve the lives of those children. This could include clothes, books, colors, etc.
Hope this helps.