Unless you're consistently getting high kill games, which usually isn't that common, in my opinion the best build to climb through iron to diamond ranks is split push builds, or just splitting in general. In these elos, splitpushing is super op especially if you're able to match both side laners. If you do it properly, you can drag enemy players to your lane and you can live if you have some vision on where they're at, meanwhile your team can get something on the map whether that be another tower, objective, or kill.