I got a writing sample in the mail today.
I'm not looking for contract help right now, but if you write better than I do I might give you a shot: smart people seek to hire smarter people.
One thing that I can do is write; another is edit. So if you send me a writing sample and there are grammatical errors on the cover page (there were), you are not in the running for anything except maybe a free writing lesson.
The lawyer who writes well has an advantage over the lawyer who doesn't. Most criminal-defense lawyers can't write worth a damn, and don't even know it. Official letters leave the Harris County Criminal Lawyers Association, bound for courts and government agencies and the media, with grammatical and typographical errors. Fortunately, most judges can't write worth a damn either, so they aren't bothered by grammatical and typographical errors. But the rest of them can, and are. It is in order to persuade those judges that lawyers should learn to write better.
To achieve that goal, buy Garner's Modern American Usage; learn your way around it. Read good writing, and when you see something that is written differently than you would have written it, find the rule in GMAU and follow it. Most importantly, write more and (this is the bit that's going to hurt) pay someone who writes better than you—it probably won't be another lawyer—to edit your writing.
[Here are two common grammatical errors that mark the competent-but-not-expert legal writer:
Phrasal adjectives without hyphens. A state-jail felony could be the same as a state jail felony. A second-degree felony might be a second degree felony. But, dammit, a criminal-defense lawyer is not the same as a criminal defense lawyer. As a matter of style, some writers omit the hyphens when there is no chance that the reader will be momentarily confused by their lack; the better practice is to use them always to signal a phrasal adjective.
Broken parallelisms. If I had written, "One thing that I can do is write. Another is editing," that would be a broken parallelism. In a parallelism, one thing ought to differ from the other only in the way that is relevant to the point. Improve your writing by paying closer attention to parallelisms. A writing sample I received today included the sentence, "He pleaded true to one 2009 state-jail-felony conviction and one second-degree felony." The first thing (a conviction) should be equivalent to the second (another type of felony conviction), but is not. This sentence could be improved by adding the word "conviction" to the end.
(It could be improved further. I would probably put "true" in quotes, since "pleading true" is a term of art. In fact, I would probably explain the effect of pleading "true": "By pleading 'true' he admitted a state-jail-felony conviction and a second-degree-felony conviction.")]