By reading (and studying & learning from) good economics-based books -- you will hopefully improve your knowledge (terminology, understanding of economic concepts/theories etc.) of economics -- and this should therefore ease you through into producing a 'better' economics personal statement ( pretty sound logic).
But where to find such 'good' economics-based books to read (and learn from) for your economics personal statement?
Hopefully right here -- well get a good idea of what Economics book to read for your economics personal statement.
But, firstly if you have not already done so, I would think it be quite wise for you to search for 'reputable economics reading lists' that are already out there -- especially those of higher education institutions such as the economics reading list presented by Oxford University and the like (and be sure to search them all and not just to the universities you applied to - be extensive!).
-- The first style/type of book I would personally suggest to a prospective higher education 'undergraduate' student of economics to read, study, learn, grasp and comprehend would actually be a second-hand undergraduate first year economics book -- and I would also believe it to probably be the most important book you will read for creating a 'good' Economics personal statement (and interview -- if you have one) from the entire economics reading list.
Ultimately they explain - the next level or in perhaps better words ... the next stage of Economics from the A Level Economics curriculum - in fact if you have done an Economics A Level you will notice a fair bit of overlap and that these books will take you to that extra step -- enough extra material, terminology and concepts to get you to another point of understanding. A point that is above that of most of your fellow applicant competitors -- I would guess, hence allowing you to demonstrate a better economical understanding than the next applicant (in most cases). They will also provide new interesting (or perhaps tedious) concepts that build on your current knowledge, that fellow candidates (competitors) are perhaps unaware of (such as the extent of the Expectations-Augmented Phillips Curve perhaps).
My personal favourite of this type of book described above is by the author David Begg with: 'Economics (The 5th Edition)' (and when buying be sure to check out the 'used' books as well they are often much cheaper) - but please do not discredit other similar undergraduate (usually first) year books, as they will be of good (and perhaps equal) value also.
And if you feel intimated by university material?
Simply don't! You really shouldn't notice a great leap in difficulty.
Now as regards to specific books -- it does become somewhat more difficult (and expensive if you plan on buying all such books from the university economics reading list - even at second hand prices), so it is important that you are i) smart in your selection and ii) actually interested in your book (otherwise you will end up struggling to actually read it -- and what you do read, you are likely not to actually grasp it fully, and if you do - it will be difficult for you to express a passion for it through your personal statement).
So far ... remember, content wise -- economic theories and concepts etc. to show you have 'extensive knowledge' of Economics comes from the undergraduate first year text book -- for these particular books however (specific economics field related books), I believe that they show instead, you have an 'extensive interest' in Economics -- to the admissions tutor. In other words, the undergraduate book shows you have the knowledge, where as referencing these sorts of books (such as below) shows you have the passion/desire/interest to study Economics (and please don't reference a book, for the sake of it! But that is a whole different subject).
These are the types of books for your Economics personal statement reading list -- that show your particular interest in Economics, whilst demonstrating and falling back on a deep understanding of economic theories etc. (from the undergraduate book). For example, if you are interested in the Development side of Economics - ' Why we have poverty? How to solve World hunger?' etc. Do a good amount of research into it (as you would have done - if you had a genuine interest anyway) and you should ultimately come across 3 main books that stand out concerning Development Economics and from the Aid Debate - Easterly's White Man's Burden, Sachs' End of Poverty and my personal favourite Paul Collier's Bottom Billion (please don't get me wrong there are some other great books on the matter also!) - all three books have rather differing (polarised!) views on what aid is doing for developing countries in Sub-Saharan Africa etc.
But, showing that you have carried out such research on an idea that interests you like 'the Aid Debate' within Development economics and that you have an appreciation for the arguments for and against (along with their common ground). And to have done this you will have needed to have an understanding and appreciation of the economic theories and concepts that coincide with the Economist's arguments on aid -- from which you fully grasp after studying the knowledge in the undergraduate text book.
Being able to comfortably discuss the aid debate as an economic component that interests you in your economics personal statement -- will surely demonstrate you as a truly exceptional candidate. A candidate who has both an economic understanding of theories and concepts, as well as a genuine interest on the matter. (Just an idea, but would it not be great to have visited such a developing country and carried out aid work there? And tie that in - you have experienced poverty first hand, trying to be a 'searcher' as Easterly terms it and helped aid a developing country through voluntary projects etc. -- What a great source of your interest in Economics? Apologies for the ramblings.)
So in short of the idea above. By reading and studying the undergraduate book (of your choice) you will have created an improved economic foundation of knowledge -- from this foundation this will allow you to explore areas of economics (such as 'the aid debate') more comfortably. From this you are then able to prove to the admissions tutor from your economics personal statement several things such as i) you have a good economic knowledge and foundation (from your undergraduate first year book studying) - that is above that of many other fellow candidates (who are likely to rely on A level material) ii) you are able to apply this knowledge to explore areas of economics, demonstrating academic curiosity iii) by writing about it competently you are able to understand such additional areas of economics, perhaps not even mentioned within A level economics - that you can commit to independent study .. and the list goes on -- a great way to demonstrate being original whilst ticking a lot of boxes for the admission tutor.
So a brief summary of the above (and what I would do)... Check for University Reading Lists (not just the universities that you have applied to, but others as well). Get hold of a copy of an undergraduate Economics text book (actually learn it!). Then through general browsing and interest (or have a similar experience to the above i.e from having visited developing countries and having questioned why they are in poverty?) - find an aspect of economics that genuinely interests you - and read, read and read more around it -- by following a brief strategy to the above you should have an excellent economics component to prove that you are a 'good and original economist', and ultimately showing that you can really think and that you go several steps further than everybody else.
If you have any comments or particularly good economics books that you recommend a prospective undergraduate economist should read, then I encourage you to please comment in the comments section below.