The MindMap below highlights the key (indeed CORE) principles which underlie the UK Constitution. If you ever need to describe the UK Constitution - these are ideas which you need to explain.
Most textbooks will set out a definition; some authorities; some examples illustrating the application of the principle. You could use this MindMap as a starting point for your own larger MindMap (great for revision purposes) - make sure that you add a brief definition (better to put it in your own words than try to memorise a quote from someone else) plus a handful of key cases and examples.
Dicey was a genius at highlighting the key ideas in such doctrines. He is summarised in many textbooks - and his book "Introduction to the study of The Law of the Constitution" is worth a read - even if it's a skim read to get you "fit" prior to an exam.
A more recent book - which can be read in a few hours - and is both readable AND full of useful definitions and modern examples is the late Lord Bingham's "The Rule of Law"