Hello, i'm a noob in need of answer that found question. The first approach with LoL wasn't really easy, i played with only 30 level (my friends) and took a difficult champion, free for the week.
So this guide is not really a guide, but some tips that could help some noob like me.

Number 1: What champion?
Yhea, i know... some champions look simply good! Some other just only die all day long... here is the problem! Don't buy hig level champion, they usually require lots of good team.
Example: recently i played as Xerath (found a really good guide and build here), but soon i discover he is much more powerfull if the team want act like that.

Just take a look to low level champion and try to pick one from all stages of prices. Try it, play it, enjoy.

Number 2: Don't look at the build!
W-what? Did i really say that?! Instead... take a look, but don't simply copy it from this site. Try to understand your champion, is weakpoint and how strong is. If you just look and take it, you'll simply waste some game.

Number 3: Buy item
Don't be scared to buy item and combine them to take more powerfull mid-late object. Lots of noob like me use all the money in basic item (expecially healt), making theyr build like a big no-sense.

Number 4: Understand you are a noob
You champions will not find full power, or position, in team untill you are on high level. So, when using your mastries point, be careful to focus on what should be our role.
P.S. Try to wait until level 20 for the runes.

Number 5: I'm a noob
Buy items... yhea, but don't waste money in ward and potion [Oh My Gank, they will kill me for that?]. Yes, you read right! Lots of noob like me thinks that some champ have simply "low healt" and they are "squishy"... never been so wrong. Don't buy the item you don't know how to use.
Example: i take a squishy one... i go like a ram on the enemy... what could do an healt potion? Simply nothing, because they are supposed to keep you in the lane, not to save your life.
You heard that some build make a huge use of potion at the start (maybe 3), but that player maybe are some pro... they are simply going to play with hardcore enemyes. Find you balance and take those item when you are ready to stay in lane longer without the recall .

Number 6: Yes, i keep my lane
Niiice, i understood how to stay top =) Aaand i'm afraid to stay bot or mid =/ Yhea... can happens... you play good in a role, but you should be able to perform all kind of game, evn to understand all the map.
If you focus on one lane you probably not watching the whole game. Maybe you are pushing hard, near theyr base... and they destroy your Nexus. Take a look to all game.

Number 7: Find your way son
Try... the best way to find the road for victory is fail. Why you died? You played well even if losing? Are you satisfied? If you answer to this question, maybe you'll find your gamestyle soon.

Little things:
If someone is strong or good, try to understand and listen to him, but think whit your mind! And never reply to hard words or flame, just don't read them.

Maybe was not a guide... but a way to help really new player find theyr way to the next level. Perform combo, read built, understand in deept, have a nice day.