Well they just completely changed the game with all of the new items and masteries so this could either be a fantastic or an awful time to start up ranked.
The number I've heard to shoot for is 80 cs by 10 minutes. Remember that this is a game that ends when you kill their base not when you kill the enemy champions. If your team is getting dived bot and you're top you need to push the hell out of your lane and start taking the tower.
Learn to buy some wards even when you aren't support and place them so that you can avoid ganks. Split pushing is really strong as long as you ward and explain to your team what you're doing.
Think about what will happen when engaging in a fight. Will jumping in actually save that tower? Or will it just give the fed Diana more gold and leave you dead so the enemy team can keep pushing?
Attitude is also really important. Focus on improving yourself and not on trying to "help" your teammates by giving them a ton of "constructive criticism." Keeping things amicable can be hard depending on your teammates, but its necessary if you want to win and advance.
EDIT: Forgot a word. --- "SR'ing is having the RNG abuse you." Deshokun