between each loss, go to your kitchen and get a light snack. Really just stand in there and think positive thoughts. I mean, just optimistic outlook kind of thing. Just stand there and kind of zone out. Remove any tilt or pessimism from your mind, and start each game fresh. This is what I do when I'm on a losing streak, and it works for me.
In game? It depends. If you think you're significantly better than your opponents/teammates, play a mage in the bot lane. My favorite being Vel'koz, but most people take brand or zyra. If you don't like that type of character, then look up guides on when/where to ward, make sure you're peeling for your adc correctly and watching your jungler's position at all times. Go roam mid at level 3 and surprise them, or go top when you hit 6 for a free kill. Remember that you're supporting your team as much as you are your adc. Again, I'm not a support main, but these are all good things to do.
About mmr, winstreaks affect it more heavily than anything else. Having a positive w/l ratio will probably raise it faster than your elo actually raises. example: if you keep a 55% ranked winrate over 100 games, I can pretty much guarantee your mmr will be higher than your rank. Especially if you win several in a row.
You should also know that OP.GG and other sites' mmr calculators aren't completely accurate. It says mine Is G1 MMR (I'm P4), but I get ~23 per win and lose ~15 per loss and play with all plat players, which means I actually have rather high MMR.