How to rise mmr?

After 7+ years of playing i still don't understand a lot about league, one of those being mmr. How does one increase mmr? How does one decrease mmr? Started off gaining 31 lp a win to 29 down to 18 while losing 9 to 12 now 17/16. Is it just mainly depended on more wins or overall how you play? I take it the more wins over losses..... But that can't be right...?
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We're testing a new feature that gives the option to view discussion comments in chronological order. Some testers have pointed out situations in which they feel a linear view could be helpful, so we'd like see how you guys make use of it.

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