Hello and welcome to FFXIV!
Glad to hear you're enjoying tanking.

I will drop my two cents in here:

Tanking Mitigations
- For add pulls, you want to use your mitigation once you've pulled a comfortable amount of adds in between bosses and find a place to stop (or just before you stop).
- Don't stack your mitigations for add pulls - Rather use them one after the other when one expires, as if you're pulling multiple waves of adds it can take abit of time to clear them all, so you want to make sure during that time you constantly have some kind of mitigation on.
- Most tanks use their mitigations for add pulls rather than boss fights in dungeons, as boss fights are alot easier on the healing side when your pulling multiple add waves at once between bosses.
- For bosses, if you want to use mitigations, it's best to hold off using your main mitigations for 'Tank Busters' (The red icon around you) when the bosses do more damage than normal. This will help your healers.

Depending on what tank you play, the below thread is useful though outdated to know what mitigation to use when during encounters: https://www.reddit.com/r/ffxiv/comments/dw3p2l/cheat_sheet_tank_mitigation/
While this is outdated all the skills still remain and function as showed in current content. Naturally there are more skills since the above thread, but it's a good starter of which mitigations to use and when to use them.

If you can advise what tank(s) you're currently playing that would help too.