Choose a username that is catchy and attention grabbing. In essence, you are competing against thousands of other singles. For that reason, your should stand out above the rest, so much so that it encourages someone to want to know more about you. For example, "50andIndependent," "ClassicalMusicMan" or "SmartIntellectualChick" will stand out more than "ImJustMe."
Avoid picking a username that can draw the kind of attention you don't want. Usernames that are sexually suggestive or explicit should be avoided unless those are the types of individuals you want to attract.
Refrain from using your real name. Though you may perceive that the site is safe, you never know who might be browsing the site with ill intentions. Once an ill intentioned individual has your real name, he can easily find out more information about you than you care for him to know, including your home address and telephone number.