Those of us working in the 10th-12th century in France and England and related families generally use the following conventions.
For medieval names, here are my naming conventions:
LANGUAGE. Please try to use the language forms that would be closest to the original language (French, German, Italian, Spanish). Sometimes forms will be found in medieval records in Latin as well, and of course each of these languages had medieval predecessors which are quite different from the modern versions, as well as regional dialects. Generally, in cases where the English translation of a word is unrecognizably different from the native one, I try to include the English version of the name or location somewhere in the name (in deference to the large number of English-speaking Geni users who may be searching for someone of Burgundy, for example, although I've rendered their name "de Bourgogne"). For men, I may put that alternate translation in the maiden name field. Some examples are Bourgogne/Burgundy, Bretagne/Brittany, etc. I always try to keep in mind what people may be using to search for a profile. Better to have more than enough search options than too few.
USE OF NAMING FIELDS FOR DATA ENTRY. (Field/input)
First name: First/given name plus disambiguating nickname or number (Charles "The Bald", Guillaume I, etc.)
Middle Name:
(1) alternate spelling of first name in parentheses as applicable (e.g. Adele in FN field, (Adelais) in middle name field. If there is something else important in the middle name field then I sometimes append the parenthetical alternate name in the first name field. OR
(2) patronymic IF there is another "last name"--e.g. FitzRoger in MN field if there is "de____" as last name. If given a choice, for French and AngloNorman names I privilege the geographic names (de ___) as last names rather than the patronymics.
Last Name: Usually a place-based "of/de/av/van _____" for medieval figures.
Suffix: Here is where to place the title (Comte de Vermandois, 4th Earl of Surrey, etc.)
For women, I put their maiden name in BOTH the Last name and the Maiden Name field. If and when Geni gives us a title field, we can move these to that field, but for now the suffix field is useful as a title field.
In cases where there is more than one place-based name (there are many children whose parents are lords of more than one place, for instance), I put the main one in the Last Name field and alternate ones in the Maiden Name field or, if there is no Middle Name, I sometimes put the secondary one in the Middle Name field. (Note: to reveal the Maiden Name field for men, it is necessary to change the gender to female, make the data entry, then change the gender back to male)
DISPLAY NAMES should repeat the essential information of the First, Middle, Last and Suffix (Title) fields. Please do not put any NEW information in Display Names since this field is unstable and frequently disappears when it is clicked upon, losing whatever information is listed there.
Remember that there are also Nickname fields (which should be renamed "Also Known As") as well as Occupation fields; these are viewable down in the lower part of the profile.