Make sure you do not use any aspect of your real name, or any other personally identifiable such as birthdates- even birth years. Your username can be searched, and anything tied to that username can come up easily.

Should I use my real first name on match com?

Again, Match.com has stopped letting people choose any username they want — for safety reasons — so it should be either your first name or a nickname. Do not include your last name. If you put in something thats not a name, you could risk being reported or even removed from the membership base.