I've written several stand alone books, mostly novellas, but the majority of my books form part of a series. This began when the genealogist in me felt the need to follow the family of my first hero through successive generations.
And so, the books of The Montbryce Legacy came into being.
With twelve books, it's my longest series. Most consist of three or four volumes, although Clash of the Tartans has six and The House of Pendray five! I have a tendency to turn trilogies into something more!
There are things you have to keep in mind when writing a series. Consistency is key. For example, you can't say Montbryce Castle has three towers in one book and two in another.
When writing about successive generations, you have to keep in mind how each character is related to the family. I solved this problem for the Montbryces by using a genealogical database to construct their family tree. Thus, I avoided referring to a character as a grandparent when in fact he was a great-grandparent.
If you don't have access to a database you can make your own 'bible" in Word and/or create a spreadsheet of birth years which will allow you to easily work out ages, etc.
A spreadsheet can also come in handy for calculating how long it will take to travel a certain distance if you know how far a horse can travel in a day.
Most noble families had Stewards who took care of the day to day running of their medieval castles. To avoid falling into the trap of forgetting which steward served my family over time, I assigned them all to the Bonhomme family.
I try to mention incidental elements in each book of a series to lend a feel of authenticity. The Montbryces distill a famous apple brandy, a cask of which often appears in the narrative.
And, of course, every Montbryce hero is afflicted with "the curse of the Montbryces"- they are noblemen in love with their wives (a rarity in medieval times).
One of the bonuses of having heroes and heroines from the same family is you can be consistent with hair and eye color if you wish. All my Montbryce men are dark haired and blue eyed (and handsome, of course.)
You can find links to all the Legacy books on the Bookshelf page of this site. CONQUEST is bargain priced at 99cents to get you started on binge reading!