Here's an example of the kind of writing that won't get you a training contract:
"I work ocassionally in a variety of part-time roles, which allows me to focus on my studies."
What's wrong with this sentence? There's a typo, for one. There's also no indication of what kind of work the candidate is doing, for how long, and whether it's of any relevance to law. Remember - all work experience can be made relevant to law.
The quoted paragraph would be much better worded as:
"During my university studies I have worked as a shelf-stacker at the Tesco Superstore in Lewisham (approximately ten hours a week). This has taught me to be comfortable in client-facing roles, and to prioritise excellent customer service, even during busy periods."
Here's why that re-worded paragraph is better: it's specific, so the reader knows what work you did, where, and how frequently; it sets out the skills used in a concise and factual way; and it translates those skills into something relevant for trainee solicitors ("client-facing role", "excellent service").
Remember that the HR / Graduate Recruitment departments of most large law firms are almost swimming in applications from would-be lawyers. Anything vague or woolly won't make the cut. Show how your work experience and extra-curricular activities make you a stand-out candidate.