One of the things I love about Jontar is their ability to adapt to any game, based on their starting position. The best synergy is with earth mana, RoK is able to build the dwarven forts (You can have 5 in a city), and with lots of earth mana you can produce a ton of resources such as gems, gold, etc... . Which is why having the fabrication guild is a must, because culture is a powerful tool for defense and for economic growth.
I have found Hephaestus to be the most powerful leaders, because of the armorer promotion, which makes his arcane and recon units better then Uxol's in the late game. (fast tracking to mithril working is a good idea). Moreover his Ability to pick philosophical as a trait makes him overpowered, I usually spam great merchants and engineers, but don't forget to build the apothecary because the potions are a must have for your top level units. (Perhaps a more fair trait would be ingenuity instead of the minor and the vein promotion)
It is always a good idea to capture as many animals as you can afford (especially hippograffs and griffons). The one problem with Jontar is expansion. I usually build around four cities unless I get a great commander in which case I will strategical place forts all over the map.
In all I think that jontar are the most diverse civ in the game. The way I want to play is by specializing each city with a specific kindred (fire, Ice, earth, nature, and a water/air). I then try to make the terrain in that city's area complement its affinity. As well I will try to set an uber unit with that cities affinity as the "head" of the city. In all this civ is a lot of fun and I think that some of the coolest scenarios could be built with them. Perhaps this summer I will try to make one.
And it is a good Idea to build 5 or more trolls in the early game, that way if you decide to get the troll elders they will be all the more powerful. I would only use them to explore in a large group though, because they are to valuable to loose at any point of the game.
I can think of several good tech paths, but I never go with one set rule I usualy just tech based off surroundings and resources.
Typically I don't focus on Arcane units until mid-late game, I will set aside 2 of my oldest jontar citizens for the arcane path. But the best way to build their xp is with valor and a great commander. I find it pointless to build them early and wait for their xp to accumulate.