Sequels, like pregnancy, are best planned...

The quickest way to succeed as an indie author these days is to write a series in a popular genre. Failing this, write consistently in one genre. (I speak as one who hasn't done either.)

I am often asked if there will be a sequel to my novels. If readers relate to your characters, naturally they want more of them. The problem is, Remix, Replica and Ice Diaries were written as stand-alone stories, and it's hellishly difficult to write a sequel you haven't planned for. We all know JK Rowling took five years to finish the first Harry Potter, as in order to write it she needed to have a good idea of what would happen in the next six volumes. This took time to work out.

Plenty of authors, after publishing a popular book, are prevailed on by readers, agents, and publishers to write a follow-up they never intended. There's also the enticement that it's the easiest way to ensure an eager readership for your next novel. And it's almost always a mistake. Here's my incomplete and arbitrary list of disappointing because unplanned sequels to brilliant novels:

• Catriona, sequel to Kidnapped by Robert Louis Stevenson. RLS remarked in the Dedication, It is the fate of sequels to disappoint those who have waited for them, and he was not wrong. I've read it long ago, and can remember almost nothing about it, whereas I can recall every detail of Kidnapped.
• Bridget Jones: The Edge of Reason, sequel to Bridget Jones by Helen Fielding, has some good bits in it, but suffers the usual problem of unplanned sequels. Having got hero and heroine satisfactorily together in Book 1, the author is obliged to split them up in Book 2 and get them together again, leaving the reader doubting this second happy ending would last. Also, to my mind, the balance of Bridget being clever and Bridget being stupid is wrong in the second book. She's too often stupid.
• The Starlight Barking, sequel to 101 Dalmatians by Dodie Smith, is...how can I put this...barking. It involves all humans falling asleep at once, dogs levitating, and a visit from an extra-terrestrial dog called Sirius to rescue Earth's dogs from the possibility of nuclear war. Weird.
• Predator's Gold, sequel to Mortal Engines by Philip Reeve. In the end, he wrote a quartet of books. Mortal Engines is a ground-breaking, absorbing and surprising read, but I'd have preferred the story to end there.

Films are no different. I only like the first Back to the Future and Planet of the Apes. The exception is Terminator 2, which I think is even better than Terminator 1. 

What do you think? Nominations?