There's a significant difference between a fresh level 30 and an experienced ranked player, even a division 5 bronze player. Granted, many of the low bronzes are down there because they are new(which is what's happening to you, incidentally), but the ones that aren't new, even though their skills are way down at that level, have a huge lead in experience on you.
The default position for starting ranked play used to be 1200 - presumably it's now still in the mid silver tier. This means that, compared to the people you're being matched with, you are probably hundreds if not thousands of games behind them(again I'm referring to veteran ranked players at a silver level - obviously there will be newer players starting out there, or falling through silver if they were carried in their placements).
In addition to just the game knowledge one acquires over those hundreds or thousands of games, they also have much bigger champion pools(far more of which they can play to a higher potential then you can), far more runes available, potentially many more rune pages, and a much better knowledge of masteries and summoner spells.
This difference is particularly evident to me because I did the same thing you did when I hit 30 - started ranked, and failed hard. At the end of season 2, I was down at about 750 elo. Since then, I switched to normals, and currently play at what seems like a low silver level(judging by borders, since I can't actually see MMR or league info for normals).
I have played a bit of ranked under the new system, and my placement matches dropped me in bronze 4. With the soft elo reset and a winning record in my placements, this makes bronze 4 way better then my end s2 elo, but the difference between that and my normals is staggering.
I still see people running clarity and clairvoyance in my ranked games, and they're not trolling - they're just so new that they legitimately think those are viable spells. They have no knowledge of team composition or counterpicking, and tend to play whatever they want in the role they get. Some of them have decent mechanical skill, most don't.
And all of this is due to being inexperienced. The players in my normals use viable champions, spells, counterpicks, and teamcomps with very few exceptions. They play better, are more aware of the map, and understand objectives. Again I emphasize that these players aren't actually very skilled - we're still at a very low level of play. The difference has everything to do with experience.
That was a pretty long post... if you want a brief summary: For best results, don't play ranked until you have several hundred games worth of experience. You can play ranked before that, but you will not do well.