The last couple of posts I looked at consistency with POV, but there are other sorts of consistency. Pretty obvious is consistency of characterisation details - if their eyes are blue on p4, then they need to be blue on p6. Watch out for words like delicate or swarthy which indicate a particular physical look.
The same is true for locations. Watch out if you've done a lot of editing because bits can be left behind without your noticing. For example, in one of my books I started with a farmhouse kitchen location. Later I changed it to a modern house with a sleek designer kitchen. I remembered to alter most of the details except the oak beams that were left in the ceiling (luckily my agent spotted them).
Then there is character consistency. If a character is coward all along, they can't suddenly be brave unless you show why. I was reading a post from Kate Walker that said the one of the main stumbling blocks for romantic manuscripts was when characters who had been at loggerheads with each other throughout the ms suddenly declared their love, leaving the reader feeling there was no basis for such a sudden change. So characters can change, but the reasons why have to be shown and the change has to be plausible ie consistent with their range. A timid person might conquer their fear and give a public speech, but they won't suddenly transform into a life-and-soul-of-the-party type in the rest of their life.
There needs to be consistency within structure too. A bit like the first post on POV, you can do what you like in terms of setting a pattern with the structure, but then you need to stick to it. So you could, for example, alternate between locations or times, or have diary entries or whatever you liked, but having set a pattern the reader would expect you to follow it. If you suddenly change it needs to be explained. At the end of Luke Rhinehart's The Dice Man the means of delivering the story has to change, but I still had a slight feeling of disappointment.
If there appears to be no pattern the reader will trust that by the end of the book you will have revealed that there actually was a pattern after all - Kate Atkinson does this brilliantly in her recent Jackson Brodie novels from Case Histories onwards. (Having said that, with Started Early, Took My Dog I'm still confused about where the stake-out at the beginning of the story fitted in. And who was the little girl in the end?)
Consistency within genre follows on from structure. If you start out as a techno-thriller, the reader will be disappointed/baffled if you end up with a historical romance. Or vice versa. That's obviously an extreme example, but there are many sub-genres even within literary fiction. It's one of the reasons why you should be reading lots so you automatically recognise consistency within the area you're writing.
Be consistent is a rule, but at least you get to set what the rules of consistency are.