ObitiuariesHelp.org and Memorial Keepsakes both offer informative guides on how to create appropriate condolence notes. Finding the right words is often difficult, but these websites offer tips and step-by-step instructions for creating respectful condolences.
ObituariesHelp.org suggests being as sincere as possible, considering the circumstances. Often a short note is best, just to say "I am thinking of you." The site also offers a sample condolence letter to use as a guide.
Memorial Keepsake provides an outline for creating a sympathy letter. The authors suggest mentioning the name of the deceased at the outset and including a mention of a special memory if applicable, then offering kind thoughts or best wishes before closing.