Your criminology personal statement is an important feature of your UCAS application, it is the only real chance you actually get at selling yourself as a criminology student.
(Please note that these are my own opinions and shouldn't be interpreted as law. But hopefully they will be somewhat informative.)
In your criminology personal statement you are basically trying to show three things: your interest in criminology, your ability in criminology and your understanding of criminology.
I believe the best way for me to get across to you as to what makes a good criminology personal statement is to go briefly over the main aspects of what you should be doing when it comes to creating your Criminology personal statement.
But be sure to do further research into conducting your criminology personal statement.
(Section One) Provide evidence of 'background' - you need to reflect in your personal statement that choosing this criminology degree isn't a short term decision, instead that you have thought about it for a long period of time and it seems like the next natural step for you to take in your academic life.
(Section Two) Demonstrate why you want to do a criminology degree - you should have a good couple of reasons as to why you want to be doing a criminology degree. Then make sure that these reasons are reflected into your personal statement - university admission tutors want to know why you are interested. However, make the reasons genuine and not clichéd.
Universities want to know that you have a genuine interest in criminology, as then they will know you are going to be committed to the course, and not likely to change degree etc.
(Section Three) Demonstrate your current ability in criminology - talk about a particular issue that is currently going on and how you feel towards it - and give a deep understanding of the issue. The more sophisticated your attitude to the topic you propose and the better you present it (e.g. using that field of wording) the higher the ability you are showing.
They want to get a grasp of your current ability in criminology - so they have a good idea as to how you will get on with the course, so it is important that your personal statement demonstrates this.
To improve your current ability in criminology is rather simple, read criminology books.
(Section Four) Provide them with evidence of your personal skills - so by stating that how you did certain extracurricular activities (and not just listing them, but explaining them) provides evidence that you have the social aspect that is also required to do a degree at university. Such things as the Duke of Edinburgh award can demonstrate leadership, working in a team, organization etc.
So now they know that you have shown that you are committed to study criminology, you have a good ability in criminology but also you have the personal skills required to carry out a degree in criminology.
Have you done wider reading around criminology - by providing evidence of 'wider reading' (which you should be doing anyway to demonstrate your criminology ability), not only will it provide further evidence that you are actually interested in the subject, and give you a wider range of topics you feel comfortable to bring up in your personal statement or an interview.
But like I have said above, your language, your use of words will be more appropriate for your criminology personal statement - as you will begin to actually sound like you a criminologist (giving the impression of a high ability in the field), as a result of reading books written by criminologists and not someone who barely has a grasp of what it actually is.
Get your personal statement checked out - be sure to get your personal statement checked out again and again, by relevant subject teachers, higher education students and by professionals (try to avoid close friends and relatives as they will give you a biased opinion). Try not to ask if your personal statement is good, instead ask how it can be improved. This invites constructive criticism, which is obviously more useful to you than simple praise.
Get it checked out by the student room - visit the forum 'the student room' online, and then head to their personal statement area. Where they have a free review system in place, where higher education students, who are often studying the subject of your personal statement that you submitted, will analyse your statement and provide you with hefty constructive criticism. Only submit it once you 'think' you have completed your personal statement.
Check out all the Universities that offer Criminology and read up on their advice for personal statements - I know in particular the London School of Economics offers Criminology as a joint course, but it goes into quite good detail as to some of the features that they are looking for in the personal statement for the criminology side of the course. They list particular aspects that they are after, so be sure to integrate them into your personal statement.
Evidence of work experience/ volunteering/EC's - The London School of Economics encourages that you mention such activities in your personal statement, do so, but make it relevant - no one is impressed by the activities by their seldom - do not list activities, apply them realistically and this will hence provide further evidence of your personal skills and ability in criminology (if relevant - e.g. shadowing a criminologist will have a positive reflection in your ability as a criminologist).
Don't worry too much if you don't think your EC's are all that great, the Universities won't be impressed by your activities, instead more so about what you have learnt from them- remember though the personal statement should be mainly be about your suitability for Criminology. (So I would suggest 3 sentences on your EC's as a maximum.)
If you are wondering what other extra curricular activities that you could do to improve your UCAS personal statement you could apply 'criminology' to the list here on how to boost your economics extra curricular activities. E.g. instead of a Economics Short Online course, look for criminology online short courses.
Check out other examples of Criminology personal Statements - obviously it would be wise to read other past criminology personal statements, and note down particular aspects you like, but don't copy anything down word for word. E.g. If you liked the way a certain person laid out their personal statement into distinguishable segments, this would be quite a wise move to replicate it. But not so to copy a line, as you will probably be caught out for plagiarism.
Also check out other relative personal statements like Law.
Before you start, Plan with a Mind Map - get all your ideas out, they don't have to make sense (you can worry about that later). Once you have all the ideas and things you want to mention organise them into roughly the three to four sections (as above - section 1 to 4 etc.), then organise the ideas by importance. This will then make it easier to actually write your personal statement (in terms of what points you want to address) and it will demonstrate that the personal statement isn't a mess and that you can organise and write with structure.
Be concise yet informative - The admission tutor is a judge, who wants you to convince them about your ability and inclination to study Criminology, but you are obviously limited by how much you can write. So the more words that you use to make a point, the less words you have to use to make other points later. Then as the more points you score, the better the chance you have at convincing the admission tutor about your suitability. Hence try to use the minimum amount of words that are sufficient to get the point across.
Back Up Your Claims - use facts and numbers, rather than subjective words. It is much better to say for example "since I implemented my cleaning strategy, the business reduced costs by 18%" rather than saying "since I implemented my cleaning strategy, the business reduced costs heavily".
Don't use quotes - they are wasting your character count, you can instead say it directly by using your 'own words' which will only take up one sentence, rather than using a quote that will take up one sentence in itself, and then another two just explaining it.
Don't try and sound clever - simply organise the evidence clearly and display the evidence. However there is no harm in showing that you understand certain 'criminology' terminology within your personal statement.
Do not use clichés - They are meaningless and they are unoriginal, with your personal statement you are trying to stand out from the crowd!
Don't use metaphors - again they are rather useless and tend to waste space, instead be direct using useful descriptions, not ones that have little meaning and are pretty subjective.
Don't talk about your A levels - you have already told them about your A levels in your UCAS application, in the qualifications area, you will be wasting your character count. Besides anything you do say will also apply to the rest of your competition - hence you won't be gaining any real advantage at all and the admission tutor will already know what is involved with your A levels anyway.
(If there is something specific that you would like to mention e.g. you got full marks in your English literature A level - mention it in the reference instead, note this is usually only worth doing if you got above 90% in UMS marks).
If you felt that you had a particular academic aspect that you want to 'show off' use different evidence - to show that you are a good writer etc., you may state that you have an award winning criminology blog for example, instead of getting top marks in your English Literature AS level.
I would also check out 'Tips On Writing a Criminology Personal Statement' - for more Do's and Don'ts and also incisive questions that you should be asking yourself.
Look up more 'general advice' for Personal Statements - there are literally hundreds of resources on how to do great personal statements, but my personal favourite however, has to be the book - How to write a UCAS personal statement.
Good Luck, writing your Criminology Personal Statement.