How many normal draft games have you played?
Do you have at least 3 complete rune pages (AD, AP, tank)? Preferably more, but this is a minimum.
Can you play every role adequately? You can and likely will be autofilled (unless support is one of your main roles).
Ranked is really not all that different from normals. Treat it the same if you already try in normal draft. If you've played a lot of normal draft and get queued with gold+ borders regularly, you're definitely ready for ranked (that was the case for me, I went 8-2 in my initial placements and got placed silver 1; although in S5 and S6 I played a combined ~130 games just to get gold each time...).
Also, if someone starts raging just ignore it (mute if you can't). Never talk back - there's no reason to tilt teammates. I've won plenty of games with a raging ally and an early deficit. As long as you stay calm, the team will follow, and you can make a lot of comebacks.
Also, the single biggest piece of advice I can give from my first two seasons of ranked:
Matchmaking is actually decent contrary to popular belief. Just sometimes you'll get a team where everyone is worse early game and better late game. These games often become stomps where you "lose pre 15 min". This really doesn't need to be the case though - do NOT tilt when allies die early. I've lost plenty of games due to watching allies die early and then getting overly aggressive trying to get a 1v1 kill to make up for it or because I felt I needed to carry. My win rate went up 10-20% when I stopped doing this and just continued playing my lane as I would, and a lot of the time I'd get super fed in the mid game with picks and my allies would know how to play the mid-late game while the enemy threw since their whole team was just good at laning phase. Keep calm - a lot of games get thrown in silver and comebacks are definitely possible.