When I got to level 30, I did exactly what you did, I jumped right into rankeds expecting to climb the ladder.
I got Silver 4 off of my promos and found myself in every game surrounded by flamers, trolls and afks.
After 20 or so games, I got sick of it because I realized that I was not having fun, and that's why I play games.
I went back to normals and was playing there for 60 games+ over the course of 1-2 months.
I decided to go and try rankeds again, and I found myself to have much better success than in the past.
So I suggest to not play ranked just yet, find a few champions in different roles and learn them. You will improve naturally.
If you're really desperate to get better now, then go into a game alone, take no runes and masteries, take an ap champion, and just farm with your auto attacks.
And don't play any games until you're getting at least 70 cs by the end of 10 minutes. In normal games, you will obviously be against someone else and wont be able to concentrate soley on farming, but if you can even 10-15 cs more than your opponent without giving any kills, then you will have a 200-300 gold advantage over your laner. Meaning either more damage, more vision, more tankyness, more utility or whatever your champion provides.