Flash and Smite. These summoner spells are the only choice on jungle Gragas. Flash is essential to making flash e plays as well as engaging lategame teamfights. Running anything else would be a little troll one could say.

For runes on graves I recommend running:
1) Reds - Hybrid magic pen/armor pen x9
2) Yellows - Armor x9
3) Blues - Scaling mr x3, Flat mr x6
4) Quints - AP x3
There are many different rune sets that Gragas can use however this specific one is the most powerful with the early/midgame meta. Hybdrid pen reds are very good as they give a substantial increase to your damage, especially earlier in the game. The 2x AS quints are important in order to clear faster however i usually run flat ap quints because past level 3 or 4 the clear will be relatively quick. Standard yellows and I personally run 3scaling mr blues just to scale a little bit better into the late game. It is vital to understand if you have many rune pages you can use ap blues against full ad teams but this is just the most optimal rune page for every expected situation.

Always go stength of ages. It is by far the best keystone on gragas however you can change Legendary Guardian to Swiftness if the enemy team has a lot of slows and stuns. The most important points here are Insight as it recudes the CD on flash. Gragas relies on flash very heavily especially towards lategame in order to engage with body slam and e combo. I go cunning instead of ferocity as dangerous game is very important in teamfights however you do you :)

Standard ability max with q first then w and then e. I actually tried out maxing w and it is pretty good against champions that get tanky faster as it deals % of hp. Overall just go with these levels up for optimal and of course - great performance.

Start-Hunter Talisman, refillable potion.
Core-Blue runic echos jungle item, swiftness,iceborn gaunlet and visage
Final Build- Randiums,Visage, Gaunlet, Swifties, Jungle item, if against heavy ap go banshees, if against heavy ad go sunfire last.

Every game is unique with different champions getting ahead and behind. It is never good to build the same build every game and follow the same build path. Some games enemy ad carry is ahead and you want extra hp and armor and some games there is a fed nidalee and lb therefore you want more health and mr.

Every situation is unique however when behind health is a very good stat to obtain. Overall be flexible with your builds, sometimes deadmans is ideal to engage fights and slow targets and sometimes you need to build locket if your support is for example a zyra who is going damage.

The only matchups that are truly hard for Gragas are Nidalee and Kindred. They can outgank and outfarm you however in teamfights Gragas counters both of these champions in the actual fights by engaging on Nidalee or simply ulting people out of kindred ult if needed.

Try to farm up on gragas until 3 and then either gank or counter jungle the enemy jungler. Jungle is all about being smart so if you see the enemy jungler top go in and ward botside, take his camps because even if he gets a kill you will be ahead in exp. You will go back and clear your jungle while the enemy jungler does not have botside or topside camps to farm since you cleared botside and he cleared topside before the gank.

Overall try to keep an eye on the enemy jungler and fight them if you are ahead and play the other side of the map if they are ahead. Always focus on taking resources and applying pressure by warding and ganking your winning lanes.

1) Use your passive well, look at the cool down of the passive and make sure to cast a spell right as it is available to sustain in the jungle
2) You can cover a great amount of distance with body slam and flash therefore try to go into a custom game and flash body slam combo to understand the limits of this powerful wombo. It is essential on gragas as it can win games by engaging lategame fights followed by ulting the enemy carry into your team. Practice will help you with this one
3)Build according to the game and never by a guide. My guide can just assist you and give an idea however you should decide for yourself, after all it took me trying all of these items to find the optimal circumstances for each.
4) Try to cancel auto attacks from buffs by using your body slam therefore saving health
5) Look at the krugs stacks that you have and see when 5 is coming up as you can auto attack the monster, barrel it and walk away with your w for some massive damage.
6) When fighting for objectives throw ur q and use w in order to have a huge spike followed by smite which ensures the needed baron or dragon
7)If worried about being invaded/want more sustain starting gromp go to wolfs and then smite blue which will allow you to gank at level 3 as well as keeping you healthy and you will have smite for blue in case for an invade. Starting krugs go to wraiths then to red which will allow you to smite red and protect vs an invade as well as gain hp back!
8) One tip i can give is to play to win however always have fun, if you are playing against a friend or a streamer do not play differently, you play your game and that is the best you can do
9) Always feel free to ask for help, add me Satanic Chaos on NA in order to ask any questions or provide feedback

Follow me at twitch.tv/letswinelo to experience my game play with me and other viewers. I will be happy to answer any questions on twitch or in game as well I am the only streamer to provide such crazy and entertaining experience. More jungle guides can be found here :
http://www.lolking.net/guides/395404 (Nidalee Guide)
http://www.lolking.net/guides/395392 (Gragas Guide)
http://www.lolking.net/guides/395498 (Kha Guide)