Zimmerit...every German modelers nightmare once you get the hang of it.
Well there are so many ways to apply zimmerit, and I probably have tried them all with varying degrees of success. Presently, I use Milliput 2 part epoxy (thanks Tony Greenland). It is a bit more messy then some other epoxies out there when wet, but it much more durable and easier to handle. It also has about a 2 hour curing time, so you have alot of time to work with it. The Tamiya Zimmerit applicator is an excellent tool to rack the zimmerit in the appropriate pattern (usually 2 mm in lenth for a proper 1:35 scale).
Also companies like Cavalier, Verlinden, and Eduard have made preformed zimmerit for various German armor. Cavalier's is made from resin and has tons of premade zimmerit's ranging from the Panzer IV's to the JadgTiger. They also have Generic patterns that you can cut to size and apply. As for Eduard and Verlinden, they make etched brass zimmerit. They are perfectly crafted and easy to apply (the fit is just awesome. So if you can get a hold of these, try em out. They usually range in price from $9.99 to $19.99.
If you ever want to gett a great lesson on applying zimmerit, pick up Panzer Modeling by Tony Greenland. He is just an amazing Master Class Modeler.