Love her or hate her, you have to admire U.S. Sen. Hillary Clinton’s tenacity. She fought her Democratic opponent, U.S. Sen. Barack Obama, D-Ill., until it was clear she wouldn’t get the Democratic nomination for president. Like her or not, the New York senator’s campaign offers women executives some valuable lessons as they fight their own battles in the world of business.

Never underestimate an opponent. The most important mistake the Clinton campaign made was that it didn’t seem to anticipate what it was up against. A first-term senator from Illinois nobody had heard of until four years ago? It should have been a cakewalk. Unfortunately, the Clinton campaign didn’t seem to have put much of an organization in place beyond the Feb. 4 Super Tuesday primaries. It lost momentum just when it needed to pick up steam. There’s no doubt that she didn’t anticipate Obama becoming the Bono of Democratic Party politics, and she hadn’t put in place the infrastructure for a campaign stretching well into the spring.

So if women execs find themselves up against their own version of a junior senator from Illinois – one they think has neither the skills nor the preparation to stand up to their brilliance – they shouldn’t underestimate him – or her.

Stereotypes are tough to shake, and they can help and hurt women in business. The rap on Clinton, almost from the beginning, was that she was too tough and played hardball – a not altogether undesirable attribute in a president. But then she had her misty moment in New Hampshire, and all of a sudden she’s back in the hunt.

In that case, being warm helped Clinton, but had warmth and likeability been the gist of her campaign, she would have been sunk. Obama has been able to be likeable from the get-go because, as a man, he doesn’t have to prove his toughness.

Women execs should follow suit. They don’t have to be likeable or warm or nurturing to get the job done. In fact, for most of them, that would work against them – and their companies’ – interests. But, when the timing is right, a bit of femininity doesn’t hurt. In fact, it can work greatly to women execs’ advantage.

Being thick-skinned is invaluable. If women business leaders think they have it bad putting up with sexism and, sometimes, outright discrimination, they don’t know the half of it. Clinton has been called every foul, vile and profane name ever invented. Thousands of hours of hate-filled talk radio have been dedicated to ruminating on every aspect of her character, marriage and physical appearance. The amount of criticism heaped upon her over the past 16 years would leave even the toughest women captains of industry curled up in the fetal position.

Now, whether women in leadership think the criticism leveled against her is founded or not, they have to admire her perseverance in the face of it. In the midst of all that, to be able to get up every morning and convince herself that not only does she deserve to be a U.S. senator but that she also has every right to be president is, frankly, awe-inspiring.

That’s something women execs should remember the next time they feel shortchanged by a colleague or don’t get deserved appreciation. At least Rush Limbaugh has no idea who most women in business are, and he saves his attacks for the high-profile targets.

Appearance matters. I hate this one, but it’s true. By most accounts, Clinton excels in this area. She is always pulled together. She’s attractive but not so much so that she risks being objectified. Clearly, a lot of thought went into everything she wore during the campaign. The good news for women is that although being attractive helps, it’s not really about having a pretty face. It’s about looking polished and professional: nice clothes, good hair and all those other things that go into looking well groomed.

But remember when she showed just a teensy bit of cleavage? It nearly shook the earth off its axis. These are the risks of trying to pull off a look that is attractive but not sexy.

Back here in the real world, take heed: well-made, flattering suits, good; figure-hugging, cleavage-showing suits, not so good. Always be pulled together and look polished, and be grateful for the lack of television cameras.

Fear not the “B” word. Women often go to extreme lengths to be conciliatory and diplomatic, all to avoid being called a bitch. If there’s one lesson learned from the Clinton campaign, it’s that being dubbed a bitch is not an instant death sentence (in fact, a “Saturday Night Live” skit almost made it seem like a prerequisite for the job). Clinton was usually quite composed, but she also showed some fire now and then and came at her opponents with both barrels. It hasn’t always made her friends, but at least nobody can claim she’s a pushover.

So whether up against a bullying competitor or a belittling co-worker, don’t be afraid to be called a bitch.

Clinton did not win the Democratic nomination this time around, but she has already broken barriers. She was the first female candidate ever to be taken seriously, and she has given millions of women a glimpse into the rewards and pitfalls of excelling in one’s chosen profession.

Whether you had a “Hillary” or an “Anybody But Hillary” bumper sticker on your car, women execs can learn a few lessons from her.

Kathleen J. Wu is a partner in Andrews Kurth in Dallas. Her practice areas include real estate, finance and business transactions.