Announce the achievement in the first sentence, and keep the wording simple. Examples include, "Mr. and Mrs. Doe are proud to announce the graduation of their son, John, from Anytown High School," and, "The Doe Family of Keswick Township celebrate the graduation of their niece, Jane Roe, from Anytown College."
Add the graduate's educational accomplishments; again, keep the wording simple. Limit the text to the graduate's biggest achievements or those that he is most proud of. Examples include, "John graduated salutatorian of his class while lettering in basketball," and, "Jane received a Bachelor of Arts in communications, graduating with honors. Jane was also active in her sorority, Gamma Delta Iota."
Include the graduate's plans for her future, such as the university she plans to attend or the job for which she has been hired. For example, "John plans to attend Anytown University this fall," and, "Jane has accepted a position with Basketweavers USA and plans to move to Seattle next month."
Don't just rely on spell check. Read it aloud. Does it make sense? Did you use the proper form of the word (they're, their, there)? This is where a thesaurus, dictionary and especially a second set of eyes will help make your announcement a class act.