First of all, you should know about LOL through watching best games.
For examples, those are listed below.
2015 LCK Spring
https://www.youtube.com/playlist?list=PLPZ7h6L6LC7XgoTJnw_8yGGxbITi_2v4L
Faker on Azubu [live]
http://www.azubu.tv/Faker
Second, play and practice. Try to duplicate what they did. In the meantime
understand why and how. Especially understand the locations of wards, GK
timing and calls for targets.
Third, select your lane. Basing on your performance, select an optimal lane for
the wins. Practice makes perfect.
Fourth, Ban/Pick strategies and the decisions. That's about good communication
and teamwork. Estimate the risk of the Elo score and make the decision. Play
or dodge.
http://en.wikipedia.org/wiki/Elo_rating_system
Final, my own trick. Use the mid lane resources to become a more powerful and
better ganker. Help your teammates to get the victory. That equals helping
yourself. Be an awesome caller and a nice teammate.