1. Void and Crippling Fear
Void has a mini-stun at night--that's the first thing we have to remember. So when facing those channeling heroes, we have to reserve our void for those critical moments. Crippling Fear, which is a silencing spell at night, can also be used for the same purpose. The important thing though, is to always be alert. When using Balanar, we should not just focus on the enemy we are "hunting." Sometimes, we overkill him/her by casting Void and Fear at the hero, and thus disregarding any other threat in the battlefield.
Balanar is a Team Hero
Let us get rid of the stereotypical Night Stalker that hunts enemies once night falls. No, he should be a team player and should be active during team pushes and clashes, where his disabling spells become most useful. Think of it this way, you only subdue one enemy when you hunt then kill using these spells. But when involved with your team, disabling two heroes at the same time may lead to two or more kills, and more survival for your team.
So next time you get hold of this ugly vampire, analyse your enemies first. Plan ahead. Who do I void? Who do I cripple? And the most important thing--WHEN? Which brings us to...
Timing
This is an important consideration when playing Balanar. As he has a meager mana pool, it is vital to conserve his spells, using them only when they're most needed. How does timing comes to play?
Well, you cast Fear to silence, right? Then never cast Fear after a nuker has just dished out his/her spells. It's useless! After the Fear wears off, the cooldown has ended too so it's nuking spree for him/her again. Bottomline: Cast Fear only when you feel your enemy is about to fight back using spells or make an escape using the same (Blink Dagger, for example).
Void, on the other hand, is used to slow enemies down. Sometimes, it's really fun to watch your Balanar chase hopeless heroes, then Voiding them to oblivion. But this is just plain childish. When you know the enemy has absolutely no means of escape, and his allies are far away, don't waste 145 mana for a finishing Void. Instead, conserve it, in case you get counter-ambushed after awhile.
Also, never, ever cast Void if you are not going for the kill. You pay lots of mana for the slow. If you are not really going to utilize it, then don't cast it. Let your other nuker teammates do the harassing.
2. Darkness
As I've mentioned above, Balanar is a Team Player. He should be one. Therefore, in my opinion, the team should make organized assaults once night falls. Instead of Balanar chasing poor Rylai once the clock hits 18:00, he should join his team and take towers down, or ambush enemies altogether. Yes, not chase loners down. It's good, yes, that you get the kills but believe me, you're doing your team more good if you lead them in battle. Augment your team's power with your Hunter in the Night and Spells. Be a team player.
Conversely, Darkness should be cast during those critical moments for your team. Say, it's still broad daylight and you need to take a base tower down. Cast Darkness then gather your teammates and break into their base. This skill may also be used as a pre-emptive spell--something that will ward enemies away from the center point (the river crossing). There's a psychological effect that whenever you turn Darkness on (what a pun!), the feeders or the "weaklings" among the enemy ranks tremble in fear. Make sure your team benefits from this "effect."
Lastly, browse the section above (Void and Fear) and think of other ways to incorporate Timing into Darkness, then Darkness with Balanar's other skills. Just please, please remember--Balanar may be a hunter, but if he hunts with the team, he'll be more heroic or hero-like. Whatever.
P.S. In lieu of this, I do not recommend Sange and Yasha for Balanar because you pay for the MS bonus here. If your Balanar is a team player, he does more hitting, and less chasing. Remember that in team battles, enemies are compelled NOT to run because if they run, they would just let their team down. So I suggest, get damage dealing and life stealing items to make Balanar the team player he really should be.