Desktop printers will vary widely, but some tips and resources on printing your product are as follows:
Print product templates are already CMYK color - the color settings for print media. While you can print RGB (monitor color) documents, CMYK is the recommended format when printing.
Resolution for printing is much higher than resolution for the computer screen. The higher the resolution, the clearer and sharper the document. At least 300 dpi (dots per inch) or ppi (pixels per inch) is recommended for print media.
When printing a 2-sided product, when one side has finished printing, take the paper out, turn it over and rotate it 180 degrees before placing it back in your paper tray and printing the opposite side. Many desktop printers will have a "Two-Sided Printing" option in their settings, and will give you instructions on how to print that second side.
Orientation: Portrait orientation is taller than it is wide; Landscape orientation is wider than it is tall.
Help your printer help you - choose the type of paper and what kind of document you're going to be printing in your printer's settings. Alignment and overall quality will be better if the printer "knows" what the job is. For example, if you're printing business cards on card stock, your settings could look similar to this:
Most desktop printers will print with a white border around your design. Often you can simply trim the borders off your paper after your design is printed.
If you don't want borders, and trimming isn't an option, take your design to a commercial printer. Many printing establishments will also accept digital files over the Internet and then mail you the finished product.
If you are printing a .psd from Adobe Photoshop, experiment with the 'Scale to Fit Media' box in Photoshop's "Print" dialog box.
Your specific printer will control final print size but you might check in the Preference settings for your particular machine. Look for a setting like 'no margins' or 'edge to edge print'.
Check your printer's Quality settings to see what's available. There will be a direct correlation between quality and speed - the longer it takes to print the better it will look.
The type of paper you use will radically affect your print's quality - use high quality paper for your final prints, and use lower-grade paper for test printing.
High-quality paper can be expensive, so investigate purchasing a "sample pack" from a paper manufacturer. These packs contain several sheets of different types of paper surfaces for a relatively low price. You can experiment on these different kinds of paper to see what gives you the best results - instead of purchasing a large amount of expensive paper and then discovering it is not suited to your purpose.