Although this book is aimed at American college students, it contains valuable guidance for students starting university in the UK. See Chapter 9 'Writing Essays: From Start to Finish'. In particular, the advice about the need for a strong thesis statement will help you to write a well-argued, strong essay.
Academic Writing Skills
This page contains guides and recordings that will help you to develop your academic writing.
An Introduction to Essay Writing at University
This 20 minute video covers the key elements of planning and writing a successful essay. It provides guidance on structuring your work, advice about how to write academically and includes tips for editing your work effectively.