When you are at level 1 : gragas will be a dominant person at the laning phase.
Although. Gragas is one of the champions with the lowest early mana in the game. Thats why you need to start to use your ability : 'drunken rage' at level 3. It will bring mana back but not that a lot. Just try to farm passively and not use your abilities on them. Always ask your jungler to get the second blue.

Farming with gragas is really awesome. Try to throw a barrel into the central of the minions wave and then directly body slam it. Your ' drunken rage" wil also help by killing creeps faster because of the extra ad bonus you get.

Gragas is really good in invading. Why? he has a really nice slow ''body slam" which slows persons 35% of their mov speed for 2.5 seconds. That would help your team really nicely in killing the opponents. He can also escape really well through the bushes by using it.

Gragas is a melee ap champion. So you will have alot of poke by ranged ap champions ( ex. lux, ahri, syndra). When they start poking you just use this nice combo before you are level 6.

First try to be in their range. Drink ' drunken rage " to have a 20% ad boost for 20 seconds.
Then try to body slam into your enemy and then quickily throw a barrel right on their spot. Then try to hit them with your boosted ad.

This damage can be really insane. Gragas is really good in trading poke.

Gragas is hard to gank. You can simply use your " body slam " to go back to your turret and be safe. When you are level 6 you can easily ult their jungler and mid laner to be safe.

When you are level 6 on gragas you will be very strong. You can easily kill them when you trade again. Now do it different.

First : drink your ' drunken rage ".
Then, try to hit your opponent with the lower side of your ultimate. This will knock you opponent to you. Then blody slam her to slow. Throw a barrel and ignite.

This will normally kill a champion if he played passive. When your building lich's ban as first item. (which is really nice ) you can even do more dmg. You will get 3 extra damage boost by using this combo.

When your team is in a fight try to throw your explosive casket in the central of all your enemies. This will deal tons of damage and knocks their whole team away. Then try to go in with your body slam, hit the enemy with your lich bane damage. throw a barrel and hit your enemy again with the nice ad boost of your lich bane.

Normally you can win teamfights easily with gragas. Thats why you need zhonya's and Roa to build ap off-tank. Try to always to be in teamfights and you will have a nice chance to win every teamfight.