Middles suck. I don't try to write middles. The whole second act is for want of a beginning and can't have an end. I prefer to think of the book in four section.

The beginning of the beginning where the rules and the world is laid out, the end of the beginning where no new information is laid out, the beginning of the end where things that have been put into play start their pay off, and the end of the end where everything gets tied up. No middle. Any new bit introduced at the end section isn't for that book, but the sequel.

Your character has to want something very badly indeed. They can't get that thing, but needs reasons as to why they can't. Solving the immediate problems creates worse problems down the road. The conflict of the immediate moment and the conflict of the overall plot should take turns being the worst possible thing.

If there's one complaint I have about all the books I've critiqued, is that the author is almost afraid to go into territory marked the worst possible thing. They seem afraid to set up an antagonist that could actually win. The power struggle, internal and external of the main character has to be upfront all the time. Far too little happens over far too many words.

Concentrate on having your main character being the driving force of the action, whatever your genre. It's about respecting the reader's time and money. They could be doing anything with that ten bucks after all their expenses and four hours after all their obligations. Let cool thing happen. Let terrible things happen. But be entertaining and the story will sort itself out as long as the first half you set up the board and in the second half, you knock everything down.