How to get back MMR consistently

I've been playing league for a while now, and was high gold/ almost plat end of last season. This season however the meta shift hit me pretty hard, and I lost a ton of games. Sure enough it tanked my MMR. According to OP.GG I've been sitting around 300 below of where i actually am for a long time. I've tried just about everything short of holding a rioter hostage to get it back up. It seems nigh impossible to win even half of my games, needless to say I've been doing nothing but falling and sitting desperate at gold 5. Is there any way i could improve my MMR that is near surefire?