Pros:

Fast and effective jungling
Area of Effect slow and speed buff
His 'E' Pillar of Filth is great for blocking paths
Very fast
Short cooldown on his Rabid Bite
He is really sexy

The jungling route is the basic route.

1. Start at blue by having someone leash it for you (Smite)
2. Go and finish off the wolves.
3. Kill the wraiths.
4. Go down to Golems in waiting for your smite cd.
5. Now use your Smite to finish off the lizard.
6. Gank!

Force of Nature VS Banshee's Veil

Force of Nature has always been my favourite magic resist item i just feel like Banshee's Veil's passive has too long cd but force of nature gives you movement speed and hp reg all the time.

Getting Warmog's Armor and Atma's Impaler is my favourite way to build my champs since you get a lot of HP you get AD and you get Armor.

Recomended

Smite is obvious since this is a jungle guide and it's not just for the damage but also to secure that you get your buff or steal their buff.

Ghost is a very good spell for trundle and it can be used in so many ways. To run away or to chase, thats why it's very good for ganks

Optional

Exhaust is good at in 1 vs 1 and chasing 1 target or running away from 1 target.

Flash is a good spell (better than Exhaust) and it can save you or help you get a kill but i still recomend Ghost but it's completely up to you what second summoner spell you want.