This subject has been beaten to death and there are volumes written on it, but since your question sounds sincere, if you want to "master" CW:
-Don't listen to it at slow speeds, at all. Forget about how much you copy and focus on making sense out of complete (CW-sent) thoughts and sentences.
-Definitely _use_ CW, and feel very free to use it at a speed which is well beyond your copying ability. Unless you're trying to save the next Titanic, it really doesn't matter if you copy everything, or even half, of what the other station sends. Legally, the only thing required for you to do is to copy the other station's callsign. That makes a contact. Everything after that is details.
-Don't listen to, or count, dits and dahs -- it will drive you nuts, and serves no purpose. Everyone who never "mastered" CW falls into this category, and if you really want to be proficient, you must learn to copy thoughts, not letters, and surely not dits and dahs.
-If you really _use_ CW (and don't just listen to it, but make contacts!), you'll quickly find your brain adapting to Morse patterns that make common words. Dah didididit dit becomes "the." Didahdit didit dahdahdit becomes "rig." Didahdah dahdididah becomes "weather" (WX). This is all mundane stuff that's part of the beginning of most ragchews. When you recognize the patterns, and thus the words, your brain will know what's coming next. WX will be followed by some report of the weather. RIG will be followed by a description of equipment. When you know what's coming next, it's easier to copy.
-Put the pencil and paper away. It's impossible to write fast enough to work higher speed CW, although an excellent typist might be able to do it on a keyboard. But it's most efficient to just listen and enjoy. If you don't write down the other guy's name, but heard it, and then forget it -- just ask him again. It's no crime to forget stuff. It's more of a misdemeanor to try writing everything down...that _really_ inhibits speed.
-After 35+ years of working a lot of CW, the only things I ever write down during casual work is the other station's callsign, name and location, in a line of my logbook. That's it. Everything else is just "listened to," and recorded in my brain; no reason to write anything else down. Writing is tiring, CW is not. If you speak with someone in person, or on the telephone, you don't write down what they're saying, do you?
-Practice sending excellent CW using a paddle and electronic keyer. Operating (making contacts) is the best way to practice, since it's interesting. Solicit reports on your sending. Unless you're already great, some of the early reports might be disappointing, but keep at it and they'll get better. It's no crime to send poorly, it's only a misdemeanor to keep doing it for a long time.
-And most of all, have fun. Practicing CW isn't fun, making contacts with it is. Make contacts. Lots of them.
73 de Steve, WB2WIK/6