New to League

Play only 2 roles until you understand them

Play 3 champs per role, don't have to build the same thing every game try something new each game

 

A Decent website that can really help if you're unsure of what to build.
This website has pretty much a lot of useful websites.

http://2ez.gg/

Also, I find the odd reddit post can crop up and give some helpful advice.
Though watching LCS/Streams can let you see what the best of the best do.

If i was to suggest people to watch they would be -

Voyboy - He talks through all his decision making, As in Items and scenarios.
Trick2G - Beasts the jungle, Really teaches you how to punish the enemy, Whilst having tonnes of fun!
Wildturtle - He's always happy, and one of the best ADC's out there.

Theres plenty of good streamers out there, Just watch a few. You'll eventually find out which ones are worth watching!