The best advice I can give you for a tri-fold a.k.a. 6 panel brochure is to remember that the inner-most fold should be a minimum of 1/8" shorter than the other folds.
So, if you had an 8.5" x 11" flat paper folding to a trifold, you would have 3 5/8" - 3 11/16" - 3 11/16" as the widths of your folds if you laid it flat and were looking at it from the 'outside'.
So, you would create an 11 x 8.5" page, and pull your guides on the outside to 3 5/8" - 3 11/16" - 3 11/16", but on the inside to 3 11/16" - 3 11/16" - 3 5/8".
I think uzzi gave you some good ideas, especially about talking to your printer first.
by: uzzidesignPosted on 2008-09-17 at 07:58:11ID: 22499438
The guides aren't so much the problem. It's that InDesign is very different from Illustrator and if it's you're first time, you may run into some other frustrations along the way. I'll try to give you a signpost for the ones that seem most obvious to me. But first, as far as guides/folds, I would find a printer first, even if it's an online one. I recommend http://www.printingforless
Otherwise, do this: Set up a mockup or maybe grab a trifold brochure from a store, like Starbucks, and measure it. Set up your document for that measurement. Set it up as a 2 page doc, for front and back, but uncheck "Show facing pages." Then measure where you'll need your folds to be, drag guides accordingly. You can set up gutters if you go to Edit > Margins and that might help too. Under File > Preferences, you'll want to set up bleeds for 1/8 in.. When you save your press-ready file, save it as a PDF-X1a or higher and make sure you check the box in the pdf export window that says "Show marks and bleeds".
Other than that, as a new InDesign user, you'll need to keep track of all your images, since they aren't embedded by default like in Illustrator. InDesign only links to them and sets up a low res preview (you can show high res previews by going to View/Preview > High Res Preview (I'm paraphrasing some of these menu titles since I don't have InDesign in front of me, not on this computer). You should periodically, and especially if you move your ID file, go to File > Package. This will save your file and copy all the links and fonts and move them to a new folder and tidy them all up for you in one place. Also, before saving your press pdf for the printer, do a File > Preflight, which will do a check for any missing font, broken links, or color issues. Overall, you'll notice that InDesign is much more particular and fragile than Photoshop or Illustrator.