If you envy Jessica Biel's buff arms, give her trainer John Walsh's push-ups a try! "When I say this is a must-do exercise, most women look at me like I'm crazy," he admits to Health magazine. "But everybody I train ends up doing push-ups at some point because they are so beneficial. They help you get incredible arms!" Get a step-by-step guide to doing them along with the exercises that have celebrities – including Jennifer Aniston and Halle Berry – in tip-top shape on Health.com!