Tip 27 : Key words & phrases
One of the first rules of non-fiction writing is to use the language of your audience, and personal statements are no exception to this.
For instance, if the job/course spec calls for good interpersonal skills, it is best to explicitly use the actual term rather than explaining that you are a "people person". You do need to be careful to do this in a natural manner, but if you achieve this important element of good statement writing you'll be in with a strong chance. It's very difficult for an employer or admissions officer to justify not inviting an applicant for interview if they have directly addressed each aspect of the job spec, in the same language, whilst also providing relevant examples and achievements in each case.
There's actually a second element to this point, and it's slightly more difficult to judge. In addition to using the same words and terms as the employer, it will also help if you can pitch the rest of your language at a similar level. As a general rule, you'll want to write in a reasonably formal manner when writing a personal statement... except in certain cases. If you're applying for a creative position, it could benefit you to write in a more relaxed, casual manner, but only if you're certain it will be well received.
The only way to judge this is from the language used in the person spec; if it's noticeably casual, you may want to consider responding in similar style.
Tip 28 : Don't be artificial
Okay, so you want to include the same language that was used in the spec, but it's important that your sentences don't come across as artificial. It's easy to stuff a load of key words into your statement, but if the result is incomprehensible gobbledegook it's not going to get you very far.
Getting the right balance is going to be a judgement call, but if push comes to shove it's best to come down on the side of natural language. If you can't find a way to use a key word or phrase without it coming across as forced, leave it out.