That’s a very interesting question Amy.
Although some might disagree, in my experience, I’d say the most important thing is honesty.
Lawyers, in popular culture, are often depicted as being ruthless and and devious, but most truly successful lawyers tend to be honest, both to themselves and their clients.
Don’t pretend to be someone you’re not, because that’s very transparent, and although some people may still use your services as a lawyer, true trust will never be there.
Whether you end up working in a firm or for a company after you qualify as a lawyer, the thing that will make you excel is honesty, which creates trust.
From the lawyers I've been around, I'd say self-confidence has to be rated pretty high (almost to the point of arrogance). And the ability to bluff with a "poker" face. Oral persuasiveness skills, debate skills. A certain amount of acting, especially if you are a trial attorney. The ability to be both personable and a jerk, usually within a 5-minute period. An ability to work long hours - stamina. I think a lot of them also engage in regular cardio exercise both for stress release and to keep the oxygen flowing to the brain. An ability to say "no," to someone when you don't want to take their case. If you are in a firm, the ability to take orders. Ability to look at the law from the perspective of what is best for your client, rather than what is absolutely "right." (someone has to defend guilty people!) A strong interest in research and writing. A strong drive to "win." And a family who understands why you work 60+ hours a week, and be accepting of that.
There are many different areas of law, so each one will have certain characteristics unique to it, however, bottom line, you will have to be able to at least appear to get along with fellow lawyers, as many cases are resolved informally, by one lawyer picking up the phone and calling the other and saying, "so, what's it going to take to get this resolved?"