This Tahm Kench guide will get you in range of your enemies while being tanky enough to distract enemies and deal huge damage.
Of course you can try this in ranked but if the opponents are smart they will give you a hard time early game. To prevent this place wards in the river and your own jungle, tell your team to keep an eye out and use pings to communicate with your teammates.
I already said the runes I recommend but health seals are pretty good for Tahm Kench as well. I don't really think you need the attack speed runes given the items you will be going if you follow this guide(you will have plenty of attack speed with Devourer and your second damage item.
Masteries are fine 21/9/0 or 9/21/0. I just like the 21/9/0 masteries since you get a good amount of attack speed in this build and with 21/9/0 every auto gets more of a kick behind it.
I explained the item choices already but you can edit it in whatever way you want (I really don't think you should get rid of Devourer because it is so much better then any other jungle item on Tahm Kench). The items I recommend make you super tanky and allow you to stick on people while applying stacks really fast so you can eat them dealing even more damage then what you are already dealing.
You can take ghost instead of flash but I don't see any other change you could really make. (with the items you have if you go with what I recommend you don't really need the speed from ghost, you probably need the instant mobility flash gives).
With this build I think the best course of action is to go for a high damage dealer on their team and just stick to that champion and eat him/her. Eating your teammates is only if you really have to (they really shouldn't be taking that much damage if you are going ham because the team will probably go for you). Given how tanky you are and your E you should be able to last a while and easily take out some of the carries. I don't recommend split pushing with Tahm Kench since you do not do that much to towers (although your ult makes it possible to split push and not worry about your team going in 4v5). If you decide to split you can even take someone with you and just ult to the team fight.
Creeping / Jungling
You wanna get that devourer ASAP but that doesn't mean you can't gank. If you can apply those 3 stacks ganking potential is pretty high especially with your Q and R. You can stun the person you gank and even eat him to deal massive damage. Saving a teammate is also very possible. You can really just farm without worry if you have ult and just get those 30 stacks really fast. Stacking devourer is very easy because of your W damage to big monsters. Clearing the jungle completely happens a lot with Tahm Kench, at this time you can go gank or just back.
Pros / Cons
-Can get to places fast
-Ganks/counter ganks well
-Early game is troubling
-Can be kited (although with the items you get to stick on people it isn't really a problem)
-Blinds are annoying