I already covered Rachel Lucas's hilarious taken on this topic with advice for the menfolk here, so I would be remiss if I didn't link to her rejoinder to the female species here. This is good stuff, especially the last line...just be honest, be reasonable, and go in with low expectations on the front end, and you can't go wrong.
1. First and foremost: NO PHOTOS OF YOUR CATS. Apparently, this really, really turns guys off. Especially if you are not even in the picture yourself, because nothing says abject loneliness and seriously flawed understanding of heterosexual men more than a photo of Mr. Furrylicious Snooperpants posing cutely on your sofa. (Yes, many straight men do like cats, don't get me wrong - but think about how lame a guy would seem if he posted pictures of his pets instead of himself....creeeeeepy. Same applies to you. And before you spaz out in a fit of cat praise, get a grip.)
2. Don't use any variation of the statement, "I'm just as comfortable in a ballcap or in an evening gown." Whoever originally invented that basic sentence might have thought they were clever but that was about 500 years ago and now it's one of the most egregious cliches imaginable. If you enjoy both casual and formal activities, just say that; don't try to be precious about it.
3. Don't announce in your profile that you're recently divorced. It says to men either that you're looking for some hot crazy post-divorce sex (which, if that IS your implication, well don't worry, you'll get it) or that you're traumatized and looking for The Perfect Man to erase all the bad voodoo your ex laid on you (which makes most sane men run screaming in the other direction). In any case, why use the qualifier "recently"? You're divorced, I'm divorced, we'll all be divorced eventually - it's no big deal and in my opinion, merits no attention at all within your profile. Just check the "divorced" box on the marital status section and call it a day.
4. Don't use as your headline, "SMILE!" Bossy, bossy. Personally, when people tell me to smile, I don't want to smile, I want to punch them in the guts, even if I was happy enough to smile when they said it.
5. For the love of all that is holy, erase from your repertoire the phrases "down-to-earth" and "girl next door". Yes dear, you and about forty million other chicks. What does it even MEAN? Frankly, maybe I should just make a list of all the bad cliches and leave it at that. The thing about cliches is they tell you absolutely nothing useful except that the person who's using them is unable to come up with a better and more enlightening way of describing themself; in other words: BORING. You're a nice, normal girl? That's great but don't resort to these stupid phrases - make an effort to describe what you think and what you like in detail. It's what I did and I got an avalanche of mail.
6. Don't say anything like, "I'm sick of jerks." It brings into question your decision-making skills: the only way you could be so sick of jerks is because you've been involved with many of them. Also, trust me, regular guys KNOW that there are lots of jerks out there. They know this because they spend 99% of their time trying to make up for it. Coming right out with the "no more jerks!" thing is tantamount to announcing that you're hypersensitive to any sort of questionable behavior, that you're going to put unnecessary pressure on any new guy to be perfect, that you're a jerk magnet...basically, nothing good is going to come out of it. Imagine if half the mens' profiles said, "I'm sick of whiny bitches." Not exactly sexy.
7. The biggest favor you can possibly do for yourself: SPELLCHECK. Or get a smart friend to proofread your profile. Do something. It seems men are even more revolted by stupid-sounding writing than women are. Profile headlines like "Let's the Games Begin!" or "Lookin for Teh One", aren't exactly going to make the most positive first impression, unless the guy himself is too dumb to notice, in which case, more power to you both, I guess.
8. Do you want to land Dr. Rich N. Moneybags? Don't advertise it. Don't list your income as $24,000-$35,000 and your ideal match's income as six figures. Are you insane? It'll never, ever happen unless the only reason you don't earn more money is because you're a 20-year-old swimsuit model/college coed. Plus, all the normal guys will write you off as a golddigger: the kiss of death.
9. Don't call yourself a "princess". You're not seven years old, toots. I don't know if men will agree with me on this, but it seems to me that the kind of woman who will say out loud she wants to be treated like a princess is going to be the worst kind of high-maintenance, demanding, black hole of neediness imaginable.
10. Be honest. Don't describe yourself as average if you're overweight (and don't forget, there are plenty of men who like the extra weight and they might not contact you if you're just average). Don't claim to have done "some modeling" unless you do in fact resemble Gisele Bundchen. Don't say you're "easy-going" if in reality you're jealous and possessive. I've heard such horror stories lately about online dating and they all come down to this point. Trust me, it's always better for a new guy to have expectations about you that are low enough to enable you to impress him on many levels, rather than have yourself built up as the perfect woman and turn out to be a lazy crazy slob just like the rest of us.
And that's all I have to say about that; I know it's half as long as the man version but I kind of blew my wad on that one and many of the same rules therein apply to women as well. If I'm way off track on any of my advice, I'm sure plenty of men will tell me so in the comments. Frankly, I don't even know why I bothered with distinct points on either of these lists I've made, because you know, it can all be summed up thusly: Don't use cliches, do go into specific detail, and please sound like you have a brain. Bammo.