Series are pluses and minuses in my book. You can continue with characters you like, you can grow and change with them; you can learn from their mistakes and they can become like friends. But if you end on a cliffhanger, you have to wait. And sometimes wait and wait! And sometimes the series is a take off from another series and you need to do a little catch up.
But the nice thing about the Baby-Sitters Little Sister Graphic Novel is that you do not have to know the Baby-Sitters Club series (the novels or graphic novels) as BSLS is younger and allows for its own story arcs. The drawback is that there are a few references to BSC, but overall you will be fine. However, it does help to start with book one (Karen’s Witch) and not start with Volume 8, which is Karen’s Sleepover. However, I bounced around with reading three-four of them and was mostly fine (but then again, I have a background in BSC and the themes are not overly complicated for the adult). These graphic novels are based on the novels by Ann M. Martin, and expand on them. The illustrations to the younger books are more bubbly and bouncy and colorful than the adaptations of the BSC themselves into graphic novels. Katy Farina has fun when they illustrate.
Just to give you a quick idea of the stories you will find things like thinking your neighbor is a witch, broken arms, friendship woes and the perils of your first sleepover when you have older and younger brothers, an older sister, a baby sister and the new cool girl who puts the eew in kewl. 
Then there is the third type of series: the series within the series. The Wings of Fire series has several novels, been adapted into graphic novels and has a series within itself. The first five graphic novels follow five different dragons and their story to save their world. When we get to Wings of Fire Graphic Novel #6: Moon Rising by Tui T. Sutherland and Mike Holmes as illustrator, we have completed that arc and start on the next generation of dragons. The themes are the same, growing up, trust, friendship, secrets, and learning from each other and learning to trust yourself, but we have a slightly different arc this time. We now follow a Nightwing (there are at least seven types of dragons), and how she is truly special and possibly dangerous. She represents the new era of dragons.
The story is fun and continues the Wings of Fire dragons stories but allows the not asked question: “What happens next?” We follow the Nightwing, Moon, as she goes through the ins and outs of keeping secrets (but then again, is there anyone who doesn’t have a secret (or ten) in these books?) and how they do/don’t make friends. The Icewings are introduced more fully this time around and we have the set up for four more books and a focus on each one of the new dragons (though we have met at least our Rainwing and two Sandwings before). The nice thing with this start is that you don’t have to know the first five books, but it does greatly help.
The art is always nice in these novels, they are busy and colorful and creative, but not necessarily overwhelming. Once or twice I had to stop and backtrack to see who was who (a few dragons look similar and/or I had forgotten who someone was). The only real issue I have is there is some fantasy violence that is not gratuitous, but tries to be edgy and might not be for sensitive readers. Yet, it does allow itself to be a mostly all aged book.