I had a hell of a time to begin with, trying to fit things onto the page and figuring out the terrible 'rotate' option, but once you get into the groove of it it's really quite simple!
One thing I would add that Carpathia missed is that, once scaled (the hardest part of pepping) and once you've added your scale factor into the [2D menu> Change the scale > Specify the scale] your pieces will all be jumbled across the pages. There is a handy little tool to fix them quickly (albeit wastefully). In the 2D menu, select [Recalculate Parts Layout] and a window will pop up, here you can change the spacing between the pieces and so forth. Once done your pieces will arrange themselves onto pages once more, but you may still have to move some around as mine tends to leave half of the pages half empty. This saves a ton of time moving them manually, and if you change scale frequently it'll become your best friend.
This is a good suggestion, although Jay's got it backwards. Never use the "Recalculate Parts Layout" option as that will re-position all the parts, making a mess and taking up many more pages than necessary; always re-scale by using the "Change Scale > Scale Factor" option. This will keep the parts in the same relative position, then you can move the parts that were on the same page in groups rather than individually.
EDIT: Just to drive my point home, I'll use the H4 Scout helmet as an example. Default, this helmet is set up with a height of 290mm; I want to change that to 300mm.
Here is what it looks like when you open it...
This is what it looks like after you use the "Recalculate Parts Layout" command...
The page count went from 22 pages to 27 pages, and it still didn't lay everything properly.
This is what it looks like after using the "Change Scale > Scale Factor" command...
You can see that the parts are still in the same relative locations, but a different size, so they take up more space overall.
By selecting the parts that occupied one page as a group, like this...
...you can move them back on to a single sheet. After just about a minute of moving them around this way, this is what it looks like...
You can see that the parts are still arranged the same way, and still only take up 22 pages. You could have gotten the page count down with the first method, but you'd be moving parts around individually. This second method is much quicker and less of a headache.
You may find that some parts no longer fit if you scale them up. If that's the case, then you go into the "Join/Disjoin" command and take care of the pieces individually.