Please correct me if I'm wrong.
The MMR system is very complicated, mostly due to the fact that it is technically a "hidden number." So far what I've discovered (both through hopeful guessing and some higher-level friends) is as follows:
Your MMR is basically a second rank that depicts how much LP you get/lose per win or loss. If you're doing well as an individual player, but you consistently get stuck with bad teams, your MMR will still increase but of course your actual rank won't. The point of MMR is to basically balance the good and bad players without relying on your wins and losses alone. If you have the MMR (or for this example, the "second rank") worthy of a high gold player, but you're in Silver IV, then you're going to be playing against and with players of similar MMR, as well as you gaining more League Points for wins and losing less for losses.
From what I've gathered, it's just evening out your actual rank with your "Second rank." If you have a lower Second Rank than your Actual Rank (ex. Silver V, Gold II, Diamond IV), then you're going to lose more League Points for losing matches, while gaining less from winning (and vice-versa), and once those two ranks get evened out, then you're not going to progress very much, and once your Second Rank surpasses your Actual Rank, then you should start gaining more LP than losing for wins/losses...
I'm in Silver V, and I'm gaining about 28-35 League Points from winning a single match, and only losing about 10-18 LP for losing, due to the fact that my "Second Rank" is higher than my Actual Rank... So pretty much, do well individually in your games and eventually you'll start gaining more LP per win.
** Again, a lot of this is guessing and I could be 100% off, so please correct me if I'm wrong. **