It just depends on a bit of factors, but my main account I'm sitting pretty in Silver 2, and I had to climb out of S4 and S3 when I started after placements. (I was in S2 before last season ended but unluckily got demoted right before so placements stuck me in S4, since they never stick you in the same one you ended on).
Anyway, last season, I was able to climb by spamming support, as I'm pretty good at it. This year, I'm trying to figure out my niche and what is good because of all the extreme changes Riot has done (masteries, runes, etc).
It comes down to the meta and what is strong, but you still need to find what YOU are good in and stick with that, and then you'll climb.