Siege Tanks are one of the most powerful and long range weapons in the Terran's arsenal and provide the best and most consistent ground splash attack. Starcraft 2 Siege Tank Tactics involve placing the tanks effectively and making maximum use of their ability to cause significant damage (plus bonus damage to armored units) in order to make the difference between winning and losing an engagement.
Once you've built your tanks, make sure you do some research on Siege Mode (since tanks are far less effective without this upgrade). This article discusses tactics for placing, protecting, and using your tanks on the battlefield to your best advantage.
The tanks have a range of 13 when in siege mode, which is among the longest in the game. You should place them in high ground locations (such as cliffs, for example) so that you can take full advantage of this. Placement is vital: the tanks need to be in the right place at the right time so you need to scout your enemy effectively before deciding where to deploy them. There are locations on every map where the terrain dictates how an enemy must pass. These choke points (both yours and the enemy's) are excellent places to position your tanks.
While siege tanks have a siege range of 13, they have a sight range of only 11. This means that you'll need to provide vision support for them using Marines or other units to best utilize their full firing range. It's also a good idea to have units scouting in front of your tanks to act as a buffer between the target and the tank.
Once your enemy realizes the potential of these tanks to wreak havoc on their ranks, they'll be looking to take them out by any means possible. This means that you'll want to avoid having enemy units anywhere in the area near your tanks. You should use your own units to swarm and surround a tank formation during times of attack in order to help keep these powerful but fragile units safe.
Tanks are usually most effective in siege mode; outside of this mode they can be vulnerable however their damage per second value is higher. To move them, however, you must take them out of siege mode. The best way to do this is to have half of your tanks in siege mode to cover the other half that are being moved. It's important to keep the enemy within range of your tanks so don't chase them too far away or you'll be constantly rushing to move your tanks.
The tanks can also be dropped into position on cliffs and this can be a highly effective strategy when attacking an enemy base. Not only is the enemy caught by surprise, but he also has to move through his own buildings to get to you while you are unleashing the tank's firepower.
Starcraft 2 Siege Tank Tactics involve placing your tanks at the best possible location, scouting effectively and engaging the enemy in a firefight (which you'll be more likely to win because of the tank's superior firepower). It is vital, however, to monitor your tanks at all times. Once your enemy realizes just how valuable the tanks are as a weapon he'll do anything to try to knock them out so keep them in a hotke[censored] group for instant access.