Think every question through before answering... be detail orientated. Everyone covered the regs already... I found that book "Everything Explained for the Professional Pilot" by Richie Lengel very very helpful for the commercial. -
Also know the systems in depth... if you get a chance spend sometime around the hangar with some of the A&Ps. Some examiners like to ask you to show them where x engine part is located... why is it there? what does it do?
On performance data... keep in mind the condition/age of the aircraft.. a 70s twin isn't going to have the same exact performance as it did when it was new... increased oil/fuel consumption, etc. What small parts could contribute to flutter or in-flight seperation? What is critical AoA? Does fuel burn affect c.g.? How(if) does lateral c.g. affect flight qualities?