One of the best ways you can improve your pronunciation is to regularly listen to native English speakers who speak with a clear and are easy to understand accent. Observe them carefully and try to mimic their sounds. Below are links to videos of British newsreaders and journalists who speak RP in some form or another.

George Alagiah

Katty Kay

Mishal Husain

Sophie Raworth

Fiona Bruce

Michael Buerk

Emily Maitlis

Mary Nightingale

Kate Silverton

Julie Etchingham