I think you're looking at cooldowns the wrong way. You say that you don't feel you need to use them - that shouldn't prompt -not- using them, it should mean "well, if I don't need them, i may as well just use them all the time!".

Generally speaking, if you know an encounter has a set rotation of nasty tankbusters, like the Hyper Compressed Plasma in A1S, or even good old Titan HM's mountain busters, you'll probably know ahead of time what they are and have some kind of vague plan on what to use when. You might Rampart one, Sentinel the next etc...

But for general dungeon tanking and easier encounters, just go wild! Pop cooldowns every pull. Try to stagger them so you only have one at a time. If you're pulling a gigantic pack of 20+ mobs in a dungeon, start with Sentinel, then after it runs out go down to Bulwark, then Rampart etc... if it's a HUGE pull maybe even open with Hallowed Ground. If you're making multiple smaller pulls just keep a foresight or awareness up. Pop Bloodbath alongside every Fight or Flight. That kind of thing.

It will just make you easier to heal, and allow your healer to relax a little. You can also do things like think of rampart + Sword Oath as being the same mitigation as Shield Oath, so if you want to contribute more DPS to a boss and arent confidant about a sword oath swap, just swap anyway and use cooldowns so your mitigation isnt borked.

My general rule of thumb is that I like to save Sentinel and Hallowed Ground for real heavy emergencies if possible (though happily blow them both on huge trash pulls if i know the party wants them). They have long CDs and generally make the most difference. But if you're doing content where you really don't feel you -need- to use cooldowns to survive, you should pop Rampart, Convalescence, Bulwark, Foresight, Awareness and Bloodbath basically -constantly-, just have one running at all times. It just makes you that little bit easier to heal and every healer will appreciate it. As Phoenicia said above, just make a point of trying to rank your cooldowns in terms of effectiveness so you pop the bigger ones during times of heavier damage.

There's no hard and fast rule on when to pop cooldowns unless you're doing really hard content where a boss has specific tank busting moves that -need- a cooldown for you to survive, and you need to have them planned out in advance. Just improvise, but don't be afraid to pop them liberally. If you're scared about dying due to not having a big cooldown when needed, just make sure you keep your biggest cooldown ready in reserve just in case and use all the others.