2. Keep Changing The Official Story
This one, it must be acknowledged, has only happened twice- both of them in response to very specific situations. That said, there's no reason to let them off the hook about it. Peri's initial exit from the show was simultaneously out of the blue, had nothing to do with her character as established, and had her initially just vanish without being mentioned. And it was
awesome. If you're going to break the rules, this was how to do it. After two years of lighthearted arguing and banter, Peri is strapped to a table, has her soul surgically removed, becomes the host for an evil monster, and then is gunned down. We did not see that coming around the time of Mark of the Rani. What made it work is that it underscored a larger point in the story - that the Doctor was indeed guilty of taking her for granted and that his carelessness got her killed. However obvious it was that the Trial (of a Timelord) was a lot of trumped up charges and there was never any chance that they would find him guilty in the end, suddenly it was clear that if he wasn't guilty, he wasn't exactly innocent either. Then of course they went and ruined the whole thing by deciding two stories later that, 'Ha ha, J.K. She's just fine and hitting it with Brian Blessed.' Then the books revealed she had brought him back to the USA to join the WWF. (No. Seriously.) Then other books said, 'No she didn't, she lived happily ever after with him as his Queen on Kron'tep.' Then others said, 'No she didn't, she was miserable and left him after awhile.' Then everyone stopped caring. The other example - after the original series ended, Ace Died, and went to the Time Lord Hogwarts, and left the Doctor to travel through time through the power of Sparkly Jewelry after having a nice pillow fight with him. (No. Seriously.) Pick a horse and ride it, people.