Thought I'd share a few tips from personal experiences using the Ganz recently:

The Ganz HMG is exactly what its name says: A HMG!
Since the Ganz is a heavy machine gun, it must be used as such. That being said, it is horrible while on the move or in CQC situations. You cannot use the same midset of an Assault Kit player when using the Ganz! It takes quite a long time to steady your aim, and even more time to get the MG accurate (after firing for a while). You have no chance against a shotgun to the face.
The Bianchi and Shuko are LMGs. They are more mobile, and are usually favored because of that. What the Ganz has is deadly accuracy and power at long range.

Let history show you how it's done!
How were HMGs used in history? They were usually stationary, covered a set 'kill zone', and were defensive. That's essentially how the Ganz must be used! You probably did not see a German soldier running and gunning in WWII with a MG42 in hand!

So how do you use the Ganz?
First, you have to be in the correct squad. If it's the beginning of a round and you're squad-bombed onto a hot flag, that big old machine gun isn't going to help much, and you won't be able to revive anyone, either. The ideal squad is a defensive one, or one that is supporting an attack, such as on a flank.
Since the HMG is not useful on the move, you must find a (generally high) defensive point where you aren't too far from a medic, but also where you can engage the enemy in a way so that the enemy is too focused on your allies to pay attention to you picking them off. The action must be intense enough on the ground to prevent wandering eyes looking up!
For example, take the roof on Tunis Harbor (2 UNCAPS, PAC side) south of Eastern Docks. You can engage incoming enemies from Junkyard crossing the barge, but you won't take too much fire (as long as you have Power Station!), as the enemy will be to focused on the apparently larger threat in front of them (which is east on the flag).
On that note, the map is key. The Ganz is only effective on certain maps, and only on certain parts of those certain maps. The map must have long sight lines with vantage points for you, much like a sniper. Tunis Harbor (with 2 UNCAPS), or the first flag for EU on Fall of Berlin are good choices. I take that back. Tunis Harbor is an excellent choice!
But wait! You're thinking that this gun must be used like a sniper rifle, and since snipers don't take tickets, the Ganz is useless, right?
Wrong.
The Ganz is like a sniper rifle in that it can engage at very, very long ranges but unlike one in that it can continue to cover the downed enemy, and kill medics that move in for the rez! It only takes a few bullets to down an enemy, and considering you have, what, 150? It shouldn't be a problem.
Even if your squad is on the move, you can support them from high vantage points (e.g. roofs). Any enemies that your squad encounters will be too busy engaging your squad, leaving you free to pick off those pesky medics.

Personal Experiences:
Tunis Harbor (2 UNCAPS), PAC side:
Defended on the roof south of Eastern Docks, as well as firing between the cracks of the fence below the roof to the west. Took NO rocket fire, picked off many lone soldiers, took many tickets.

Fall of Berlin, EU side:
Defended in the building between Crossroads and Roadblock. Mainly stayed in the southern corridor (NOT THE CENTER! THAT'S A KILLZONE FOR APC MORTARS!!!). Very easy to cover the main road and ladder entrance to the flag. Was able to stop many rushes on the flag (kill enemy SLs in the hallway above the ladder, kill enemy SLs hugging the building on the main road) and was able to quickly respond to breaks on the northern flank. 20 kills, 22 teamwork, 1 death. EU didn't lose a single flag.


In summary:
-Use the Ganz HMG like a HMG.
-Stay back, away from the frontlines, but not too far from a medic.
-Get high vantage points, and attack from a distance.
-Be sure you're in the right situation; light to moderate defense is the best role.
-Be sure the map is favorable (there are only a few!); long sight lines, roofs, cover, all away from the frontline.

And if you took Zhohar's Basic Tank course, you can pretty much apply it to the Ganz.