Memos can be the easiest piece of correspondence that an administrative professional will ever have to write. It is important to just keep formatting standards at the forefront and grammatical errors at a minimum. Always make it a point to edit and proofread your memo prior to sending it out.
It might be a good practice for you to prepare a draft version that you could circulate to someone that you trust who may have excellent editing and proofreading skills. This individual may be able to catch errors in which you missed. Once you get the draft version of your memo back you should make any necessary changes, and then put the memo into a finalized version in which you can disseminate to the proper recipient.