While positioning is one part of tanking, poor gunnery practices will get you killed just as easily as poor positioning. The first thing to consider is trigger discipline. Tank weapons are loud and easily recognizable, as are the individual projectile types. Firing when you don’t need to will instantly telegraph your position to any smart enemy drivers in the region, and they will react accordingly. Take a moment to line up shots carefully. Many drivers fall into the trap of shooting the second they reload, which can be exploited by vigilant opponents. Here is an excellent example: https://www.youtube.com/watch?v=8lCsZuuKPtQ
Likewise, aim is obviously very important. Tank shells, especially HEAT/HESH types, are slow and have significant drop. Understanding how to lead targets at range is critical, and this can really only come with experience. Practice in VR training can help with estimating ranges, as will an understanding of the gunsights.
Lastly, it’s important to know the difference between the three shell types. The default HEAT shells have high rate of fire but low individual shell damage and poor ballistics. AP shells have high alpha strike damage and excellent ballistics but poor splash and a long reload. HESH combines the worst of both worlds, with poor ballistics, mediocre direct damage and decent splash damage. In practice, AP is generally the preferred choice for most engagements due to its improved ballistics, though HEAT can be viable in certain circumstances or with specific close quarters play styles. HESH is really only good for farming infantry kills or directive completion.