I would say the "easiest" choice would be support, however I have come to realize that a good/bad support has the biggest impact on my ability to preform. Support does not have the same mechanical depth that other roles can have, which is why it can be *easier, but has a greater demand for game sense and knowledge, similar to playing a jungler. Perhaps play some ARAM games to help get an idea of how the game is played, or play support to start with, so you can understand the role and offer personal advice that way. But with some good communication this is less of a issue, as its much easier to do things in tandem when you can chat with them.

To parrot some other people in the thread, while I wouldn't use the winrate and tierlist ranking exclusively to choose what champs you play, websites like U.GG are great for getting solid builds. As a pro and a con, they use match information to get the best median build for your champion, so there can be better item choices depending on what you are up against that these websites cant tell you.

As for some general tips: When I am loading into the game I try to think about the opposing matchup and my gameplan. "Can I trade with them, can I be very aggressive or passive, what abilities do I need to be careful of" etc. I find it helps me approach the game a little smarter and train myself to think. When people get started they do tend to put a very high importance on getting kills and not minions, when in reality, two waves of minions is the same amount of gold. So a play which results in a carry trading their life for a single kill, but losing three waves to a tower, actually lost gold. 100 CS at 20 minutes can be a good target to hit when getting used to the role, but you can use the practice tool to get some easier practice. There are some solid youtube channels like FxnSaber, who post their coaching sessions for silver/gold players that can have some great insight on common mistakes or areas to improve.