When using InDesign, a great way to make sure your printer will receive everything they need to correctly print your document is to create a "Package" containing all of the necessary files. Fonts, images and other necessary items are put in one folder that you can easily send to your printer.
InDesign does this automatically with it's "Package" function. To package your InDesign file, open your document and click File > Package... In the dialogue box that opens make sure there are no missing fonts or images and click the "Package..." button. A window will open that asks for contact information; this will create a .txt file that the Prepress department will use to contact you if there are any issues. Click "Continue." Give your packaged folder a descriptive name and choose a location to save it. A folder will then be created with everything the printer will need.
The Package dialogue box has several menu options that will help you ensure all fonts and images are linked or embedded, and that the colors are correct. These options can help you locate issues in your InDesign document you may not have been aware of.
Information about the document is displayed here, including any errors that are found (such as images that are not in CMYK, missing fonts and images).
This lists all the fonts that are used in the document. It tells you the name of the font, what type it is (postscript, truetype, etc), and if it is present or missing. If there are errors select the specific font and then click "Find Font..." to see available options. You can change the font in the "Find Font" window, if you wish. Each instance of the original font will be changed to the new font you specify in the "Replace With" section of the "Find Font" dialogue box.
This section will tell you if there is anything wrong with your images. Make sure there are no missing images (if there are, select the image and click "Relink" to find the image). If you have images that were created in the RGB color space, a warning will appear here. You can edit your images in Photoshop or Illustrator and convert them to CMYK if you wish, or you can let your printer's Prepress department do this.
Process (CMYK) and spot colors are listed in this view. You should see Process Cyan, Process Magenta, Process Yellow, and Process Black. If there are spot colors listed you may want to go back to your document and convert those colors to process, unless your printer knows you intend to use spot colors. You can change spot colors in your InDesign document by canceling out of the Package window and right clicking on the spot color in the "Swatches" palette. Select "Swatch Options," then change the Color Type to "Process." Go back to the Package window by clicking File > Package...
These are a list of settings and plug-ins that are used in the document. They cannot be changed in the Package dialogue box.
For more information, visit Adobe InDesign's Help page