Taken from the .gov website.

As a director of a limited company, the law says you must:
try to make the company a success, using your skills, experience and judgment
follow the company’s rules, shown in its articles of association
make decisions for the benefit of the company, not yourself
tell other shareholders if you might personally benefit from a transaction the company makes
keep company records and report changes to Companies House and HM Revenue & Customs
make sure the company’s accounts are a ‘true and fair view’ of the business’ finances
register for Self Assessment and send a personal Self Assessment tax return every year