Polite: Please write the report for me by tomorrow.
Even more polite: Please could you write the report for me by tomorrow.
Polite form: please + verb (bare infinitive) is ok, but for British people even this can seem too direct, especially at work.
Even more polite form: please + could + subject + verb (bare infinitive) – using ‘could’ makes everything more polite. In a British work setting, this feels more comfortable.
Polite: Please open the window.
Even more polite: Please could you open the window.