Vlad's ganks are the strongest but they aren't weak. His ganks are very dependent on his pool which is his only CC but it's on a fairly low CD so even if you don't get the kill or somebody flashes away you can just try again. Look for players who are out of position then walk toward/behind them and go into your pool to slow them and then follow up with E+Q. After 6 you'll want to initiate with your ult and then pool so that you and your teammates get the full benefit of the %12 damage amplification. Vlad can also tower dive quite effectively either by diving for a kill and then pooling to drop tower aggro right before he dies or by going into a pool to avoid all aggro and then opening up with a combo for the kill. If you plan to dive be sure to have an out or have a teammate or minions nearby onto whom you can transfer tower aggro. (Note: Ignite will continue to damage you after you go into your pool)

There are different build routes that you can go but usually you'll be a sustained damage off-tank mage. Try to land your ult on as many targets a possible to give your team amplified damage and always keep your E at 4 stacks to get the maximum possible spellvamp and healing. Position yourself to zone away their carries while landing your AOE damage on as many targets as possible. It can be tempting to W into a fight to get on the carries or land a slightly better ult but Vlad lacks burst to blow people up and you'll have no escape if you get caught after your pool times out. Try to save your pool for when you're really low for the maximum possible effect. If you dish out enough damage and zone their carries away from the fight, you can usually get the enemy to dedicate a lot to killing you, only to turn into a pool and casually stroll away.

With %6 spell vamp and armor marks Vlad can sustain reasonably well in the jungle. Spamming E in the early game is usually not advisable since you won't get the HP back and you'll have to base sooner. Vlad's pool does not work when you're alone since it makes you untargetable and resets monster aggro. You'll almost always want to rush SotAG since it supplements Vlad's weak clear speed and sustain. From a jungling perspective the biggest powerspikes Vlad gets are SotAG, Deathcap, and Zhonya's. Each of those items adds a lot to Vlad's sustain and clear speed. Vlad can't solo Dragon or Baron very easily so focus primarily on farming and ganking.

If you're being counter jungled you'll want to rush your Quill Coat for the extra ward. Buy wards and extra potions. You can put a pink ward in the river-side bush behind your red buff. Vlad doesn't have much CC outside of his W which requires you to be in contact with somebody so it's easy to get caught out by early-aggression junglers like Lee Sin, Warwick, J4, Elise, etc. If you can't escape or get to a nearby ally in time, you can try fighting as you work your way toward a jungle camp and when you're low HP pop your W. You'll get the spellvamp back from your W on both the enemy champion AND the monsters and the enemy champion will get the monster aggro and take some extra damage from them. (Note: That trick only applies to the early game since mid-late game champs can get back more HP than they lose)

Vlad has no real escapes if he gets caught out so the only time you'll really want to be counter-jungling is if you're ahead and snowballing or if you have vision of all of the enemy team. There are certain champs that Vlad can usually counter-jungle effectively and these are your tanky, mage junglers like Amumu. You can reduce the risks of counter-jungling with good ward placement. Always be sure to save your W for the escape.

This is a video by Diamond elo jungler Foxdrop who plays on the EU West server. It outlines effective warding locations as a jungler. https://www.youtube.com/watch?v=xH_ysOhyLeI