I by no means have done well, I promo'd into Bronze 3, made it up to silver 5 twice and now I am at 93LP in Bronze 2.
What I find is working your MMR to your advantage. What I mean is my MMR is up and down oscillating, that correlates to streaks in wins and losses. I would get on a 5-7 game losing streak and drop a rank. Your MMR is pushing you to what rank it thinks you should be at. When my MMR was on the down swing that is when I would get the team composition that was unwinnable. Matched with members on my team with lower ranks then I had and the opposition team with higher ranks.
When you lose a game, stop playing. I find by stopping and not playing a ranked game until the next day those losing streaks don't happen. Also look at what time of day you play, what is the demographic of players you are most likely to be playing with? If you find you always get the AFK's and Trollers at a certain time of day, avoid that time.
Duo queue, Duo queue, Duo queue, every 3rd or 4th game if you can and with someone you have coms with and know.
If I am winning; keep playing until you get that loss, then stop.
I focused on a roll and three champs in that roll, how to play them in different situations, how to combo, how to set up other members of the team. Different item sets that make sense for the style of my play not just what is the best META.
Good luck!