This will sound paradoxical but the best way to gain speed is to slow down.
I've spent my life on keyboards of one kind and another but when I learned to type in 1954 I was truly awful. One of my tutors said, "You're trying too hard. Slow down. Sit up straight. Get a rhythm. That rhythm will give you speed."
It works. Try typing very evenly. You can hear your fingers tapping the keys tap-tap-tap-tap-tap very, very evenly. You do that for a month and you'll be surprised how fast you are typing.
Oh yeah. Watch your posture. You'll never be a speedster if you slump in your chair.