With both in the semifinals at Wimbledon, Serena also looks for some kind of edge.
"She's an opponent," Serena said. "You scout your opponents."
Before the two can meet in the final for the third time at the All England Club, they have to win today.
Serena will have to get past Zheng Jie, of China, and defending champion Venus will have to beat Elena Dementieva, of Russia. If both Americans win, they'll play in the Wimbledon final Saturday for the first time since 2003, when Serena beat Venus in the championship match for the second consecutive year.
"She won last year," eight-time Grand Slam champion Serena said of Venus. "But I'm not going to sit here and say she's the favorite when I'm still in the tournament. That's not me."
Serena is 8-7 against her sister overall, but a dominant 5-1 in Grand Slam finals.
"We're extremely motivated by each other, win or loss, on or off the court," said Venus, a four-time Wimbledon champion.
On Wednesday, the sisters beat Sania Mirza and Bethanie Mattek 6-4, 6-3 in the women's doubles quarterfinals, whispering tactics to each other on occasion but otherwise keeping calm despite trailing 3-0 in the second set.
Dementieva, Venus' next opponent, struggled for long periods before beating Nadia Petrova in three sets in the quarterfinals. But she's not worried about her next match.
"She's the defending champion. It's all pressure on her," Dementieva said of Venus.
Zheng, ranked 133rd, is this year's surprise in the women's draw, reaching the final four with a run that includes a third-round win over top-seeded Ana Ivanovic, the French Open champion.
By beating Nicole Vaidisova, Zheng became the first Chinese player to reach the semifinals at a Grand Slam tournament.
Serena won't be taking the 24-year-old player lightly.
"I've been watching her play," Serena said. "I think she's doing a fabulous job, and I don't think it's luck."
Serena and Venus have won six of the past eight Wimbledon titles. Neither has dropped a set so far, and their power games have set them apart from the rest of the women's field.
"I've been working really hard lately. I'm just waiting on the results to come," Serena said. "I deserve this, because I don't think anyone's been working harder than me, except for maybe Venus. I mean, that girl works even harder than I do."