Any tips on how to carry?

I'm currently in gold 4 but have reached as high as gold 1 in recent weeks, i have this constant cycle og games where i win loads and lose loads which is really keeping me from climbing consistantly well in platinum which is my goal this season. I also switch roles a lot but mainly play mid/jung as well as some adc. What i think i have identified as being my weakness is not being able to carry well even when ahead. Although this is not as much as a problem when im adc when im mid especially i can find myself miles ahead of my teams with kills and good cs, but i cant translate that into a win. If you are curious I play alot of ad assasins and sustain ultility mages like oriana, viktor and cassiopeia. Any tips general or specific?