Whenever possible, get your charity's marketing materials printed professionally, as office printers will not produce the same quality of printing. This is particularly the case if you are printing in colour, doing large batches, or producing a leaflet with multiple pages or folds.
Research potential printers for your charity on the internet and get a quote from a few printers. Local print shops are usually more expensive than online printers, although the extra cost may be worth it for a personal service.
Make sure the printer you chose doesn't simply do digital printing - otherwise the quality won't be much better than using your office printer. Ask for Lithographic printing - this is cheaper than alternatives, such as Letterpress and Thermographic.
The printers will want to know from you:
The 'Basics Design: Print and Finish' mentioned in the recommended books section, has good basic information on the printing process. Another good source of information is the International Paper Knowledge Center website, which provides information on various topics, including types of paper folds and binding methods.