PRACTICE, PRACTICE, PRACTICE
As with anything in life that you want to be good at, it all comes down to practice. Results don't show up overnight but over a sustained period of dedicated application. And the best way to build practice into your life is to ...
MAKE IT A HABIT
If you just say to yourself, "I'm gonna practice my reading this week -- I really mean it this time," the week is likely to come and go (again) without you ever cracking that book. But if you say, "This week, on Monday through Friday from 7:00-7:30 pm, I'm going to sit in my favorite chair with [book that I'm really excited about] and try to get through X number of pages," your odds of actually doing it go way up. Best of all, before long it becomes second nature: instead of having to force yourself to sit down at the same time every day, you'll find it feels strange NOT to.
PICK SOMETHING YOU LIKE
The best way to keep yourself practicing anything is to find the joy in it, and reading is no different -- so choose something you think you'll like. When I was going through a Stephen King phase in high school, I had a teacher scoff, "It's like chewing gum for the mind ... there's no substance!" Maybe, maybe not, but who cares?! It doesn't have to be "great literature" ... it just has to be fun!
GET A READING BUDDY
Find someone who wants to read the same book, and challenge each other to get through chapters so you can talk about it, the same way you would about Game of Thrones or anything else you love. Even better: do it together, in the same time and place, so you can really hold each other accountable.
SEE, DON'T HEAR
Many people, when reading, hear themselves actually saying the words in their head as they go along ... meaning you're only reading as fast as you can talk, which is a fraction of the speed you're actually capable of. This is called "subvocalization," and you want to train yourself out of it. Instead of hearing or listening to the words, try to visualize what the words represent, and suddenly the book will become a fast-paced movie in your mind.
"CAST" THE STORY WITH YOUR OWN PEOPLE AND PLACES.
This is similar to the memorization technique called a "memory palace." Here's how a memory palace works: in order to memorize something -- say, items in a long list -- you envision yourself walking through a familiar environment, such as your house, and "placing" the different items at locations in the house. The premise is that, by linking these new items with places that are familiar to you, it will create associations that you can hold onto. The same idea can work when you read. If a new character is introduced, maybe imagine that she looks like your second-grade teacher, and it might be easier to remember the things she says because she has a familiar voice. If the book takes place in some grand mansion, maybe it can look like that art museum from that class trip last year, and you'll remember that the first scene in the book happens in the room with your favorite painting on the wall.
Whatever you do, recognize that your "inner reader" will really kick into gear when reading is not a chore, but a pleasure. If you've never liked reading, I can practically guarantee you it's just because you haven't found the material you click with or the reading habits that work best for you. So if this sounds like you, keep looking ... and keep reading!