Well it's quite simple: keep practicing and try to type as accurate as possible, I know this is maybe not the magic formula you are hoping for, but that is actually it what helps. I switched my layout to Colemak, and got about 20 WPM faster than before, but that step is maybe not for everyone as you have to start from the beginning again, and it does not help everyone to improve their speed that much.

Honestly I have been typing my whole life and do it at my day job, and that helps. Practice is definitely the best way to get better at typing. As long as you are typing correctly (using all your fingers on the home row, etc) you should get better just from practice. Just don't expect massive increases in speed quickly.
I've also hit a threshold in my typing speed, however I notice bit by bit that I've been getting slightly better throughout time!

I would say that once you don't have to worry about your fingers moving and can type just through muscle memory, it becomes a lot easier to type quicker (through practice, of course). I would bet reading a lot helps typing as well, as you don't have to think about spelling or grammar as much when typing out words.

I looked at your profile, you seem to be improving gradually already. But I imagine you're frustrated with your progress. So was I a while ago, but now I changed things up. I started playing Instant Death Test, which punishes inaccuracy greatly. It was very frustrating, but I was molded into the hunk of a man that I am today.

I would heavily recommend not relying on muscle memory. It's good for commonly used words and letter combinations, however it is -ass- at complicated combinations or new words. Focus on accuracy!

WHAT A HUNK, absolute unit of a man

*Notices buldge* Owo, what's this?

Impossible. 60wpm is human limit

I have tests with 120 words per minute, trust me its possible. Just practice and type a lot. Memorize where every key is so that you can type a sentence on an air keyboard.

I find that I make the most improvement when I have a session for so long that my average speed actually gets down to 20% or so less than my normal average by the end of it (compared to my average speed) no matter how hard I focus or try. After sessions like that I take at least a few hours off. I only do two of those per day at most. But after doing those for a few days in a row, then taking a couple days off, I always find it much easier when I come back.

It's also worth noting that the faster you go, the harder it is to increase your speed. So the jump from 55-60 wpm will be harder than the jump from 45-50, but will be easier than the jump from 85-90

OWO, is it a cub, monseigneur?

I'm pretty sure he said that 60 is the limit as a joke. The OP said he typed 63.

Play osu mania xd or something like that

I typed a more extensive reply in another thread, but I'll summarize the main points here.

-chunk words as you read them. For words that you can't chunk, practice these words in isolation until they feel natural (remember how easy it is to type that complex password you have? The same can apply to other tough words.)

-read a lot. There is a good reason why you can type faster in your native language---this ties in with your ability to know how a word is spelled without having to carefully read each letter of the word. The more words you know, the more words you can chunk, and the more words you can chunk, the faster you can type.

-accuracy is good---perfection is often overrated. Try pushing yourself now and then. 100% accuracy is usually more accuracy than most folks may need. Decide what error level you can accept for yourself, and then try pushing yourself to make your fingers move faster. You may be surprised to notice how much you had been holding yourself back in your pursuit of 'perfection'.

-keep your fingers warm and nimble. I find that fingers can get cold without us noticing right away. When fingers get cold, they get stiff and slow, and you start to make more mistakes. Take the time to soak your fingers in warm water, and you'll be amazed at how much better your typing feels afterwards. Keep your fingers flexible by stretching them (gently) now and then as well. Avoid popping your knuckles too much though!

-practice a lot! Obvious, but still needs to be stated.