This is my first guide in Mobafire. So i apologize from before that my guide wouldn't be that good. Still I will try my best to make a good guide on garen.

Get 1 point in Q then E then W. Max E and then Q then W.
E is great for farming and the combo kit is really great.
Combo
Q (Silence) --> Basic attack --> W --> E --> Q ( Activate Q 1~2 sec before your e gonna end) --> R(if below 350-450 hp) and ignite wherever you get the chance before R though.

You need to position R well because the Cooldown is very high. 153 sec at lvl 6.

The items i listed above are for against all champs.

Aatrox - Never ult to kill him, anyone would leave track of his passive and waste it. Otherwise easy to farm against.

YOU CAN WIN THIS LANE

Ahri - Easy. Just dodge her charm and farm with e. Get giants belt before chain vest for this lane.

YOU CAN WIN THIS LANE

... too lazy..

YOU CAN WIN EVERY LANE

Thank you for giving a look to this build. Its bad but I hope it helps you in any matter.