A personal statement is a summary of your abilities. It's not about what you have done, jobs you have held, qualifications you have gained or your experience - that's in the rest of the CV. This is about the transferable skills that will contribute to the job. As in the covering letter, you need to gear it to the position you are applying for - and the clues are in the advertisement. Stick to one paragraph of three or four pithy sentences. Go through the job specification for the new post if you have one and make a list of the skills that are required. Make every sentence count. Be relentlessly positive and avoid negative statements. You need to give the prospective employer a snapshot of what you are like professionally. For example:
My previous jobs include two years as a sales assistant in an organic food shop in Japan. This has given me experience of dealing with customers, as well as cashier skills and a basic knowledge of food retailing. I have been living in London since last September, and am currently studying English at a language school. I have good English communication skills (recently I passed the Cambridge First Certificate in English exam). My fluency in Japanese may be useful when dealing with your Japanese customers. I am an enthusiastic worker, and enjoy working in a team. My student visa entitles me to work up to 20 hours per week (or longer during my school holidays), and I could start work immediately.