I played a few scores of games as Garen and vs Garen, and what i had noticed is that no one ever builds him to capitalize on his strengths. Common superstition is that Garen is "tank" and thus people stuff him with Warmogs and whatnot. Which is foolish, same as no ap Amumu.

Runes are almost all scaling, for maximizing gained stats because early game for Garen is easy. Greater Mark of Scaling Attack Damage Greater Seal of Scaling Armor Greater Glyph of Scaling Magic Resist synergize well with his Decisive Strike and passive from Courage, Greater Quintessence of Gold are a must because his items are expensive and extra 500 gold on top of succesful killsteals and farm is good.

Standard 9/21/0 with emphasis on health and slow reduction - never can have enough of it. Once escaped from Jax and Nunu across all map.

First item is Doran's Blade - some useful stats plus you can heal off creeps. Berserker's Greaves first if you have trouble landing your Decisive Strike. Now why not Boots of Swiftness? Because with your speed buff 15 moar ms are redundant and you have slow reduction from masteries and slow cleanse from Decisive Strike. Vampiric Scepter first if you get bullied by some spammer like Yorick or Jayce. Zeke's Herald next, because no one builds this OP item and you need cdr. Then Black Cleaver for more cdr and Avarice Blade so you start saving for Infinity Edge. On average, here is when game ends, but if it doesn't because of your feeding "teammates", you can top it with Youmuu's Ghostblade to chase feedies much better.

R>Q>W=E. Lots of speed first and Spin-to-Win or Courage depending on whether you lack damage or tank.

Heal and Barrier. No alternatives. For mobility you have Decisive Strike, for KSing your Demacian Justice - quite poetic are their ways of judging people, are they? DAMACIA!!! and Exhaust got a serious nerf. Barrier negates Ignite and Heal acts as backup and towerdive protector. You can bait someone under tower with 100 hp then BOOM tons of hp out of blue sky. Saves from anything short of dedicated 3-man towerdives.

You get the top lane, bar that go support. Unfortunately, Garen fails as a jungler due to his passive not working on monsters.

In lane you first click enemy champion then press Q, otherwise it may misfire on minion. If he runs away, you blast Q on low health minion - win-win. If there's some retribution coming, press W. Use spin-to-win to clear overflow before it reaches your tower. Generally you don't care about pushing, you have to utilize heal from Doran's Blade. If you pushed a small wave to his tower go farm nearby neutrals. If you amassed a huge wave theres a fun tactic that got me some kills - you go attack tower and press W. Hurt that your minion mob dishes to enemy far exceeds what he does to you and may bring him low enough for kill.

Generally you do not need help from jungler and not in danger of enemy jungler ganking. 3 man gank is another story and they will do it.

As support you dont bother with wards - whoever needs them should buy them. Whom they will kill - some squishy or sprinting over9000 hp monstrosity? Blame your "carry's" deaths on her stupidity and inbred affinity for feeding. Good rangers have zero deaths without wards.

In teamfights your duty is to hide in nearby brush or go farm something. Then, while everyone is busy feeding, you scream DAMACIA!!!, charge from behind - for added confusion - and secure some kills. That guarantees your immortality in most cases, no one sane will attack over9000hp monstrocity when there are low health feeders available.
Never ever participate in stupid stalemates under towers - no farm and risk of some Malphite or Fiddlesticks accidentally murdering you.

Try to solo as much as reasonable, and you will be 2-4 levels above an average bunch of feeders.

For target prioritization go for KS but remember that you have silence - Katarina ulting you is unhealthy.

When you finish your Ravenous Hydra you can solo dragon and take lizzard as often as possible.

Pros:
- DAMACIA!!!
- Excellent KSer and farmer
- Potential immortal
- Well suited for any team composition and all maps

Contras:
- Hard countered by Feeders Failurers FUBAR
- Does not have outstanding features like instagib LeBlanc style or OP CC
- Haves an average win ratio