loosing weight tips

I am currently 20years old and weight 20stn, I recently got engaged and I am really wanting to loose weight before the wedding and so when we start trying for a child after the wedding it will make thing easier as I know sometimes it's harder when you weigh more. Has anyone got any HELPFUL tip on how to loose weight and keep at it as I have tried before and given up and I really want to do this for us! Thanks in advance ladies! X