My tip to improve your typing speed is to...
Remember that there is a professionalism in typing. Why is this important? Since typing is similar to learning a sport or a musical instrument, then the same rules of development apply. Remember, an amateur is someone who practices until they get it right. A professional practices something until they can't get it wrong. When you get proficient at typing you'll find yourself accidently hitting the right keys.

When my fingers hurt after too much time on the keyboard, I...
(a) Take a break
(b) Review my posture and hand placement.

My tip to improve your typing speed is to...
Going from '"one-finger typing" to "touch typing" has a noticeable difference that no one talks about: you physically feel comfortable with the keyboard when you learn to type. I can only compare this to playing an instrument like a guitar or piano. This is also like getting better at a sport like catching a ball or swinging a bat. I think people overlook this when they use something like "muscle memory" to describe typing proficiency but this is what should be emphasized.

What really helped me improve my typing speed is...
(a) Focusing on accuracy. After reaching a plateau keep accuracy above 97% and veerrrry sloooooowly my speed increased. Don't focus on typing speed.
(b) Trying to focus on the next words to be typed. This subconsciously prepares me for the next word