Big Bear Butt made a post about how he uses trinkets. I do something similar to that on my shadow priest to maximize their use.
On my tankadin and rogue, though, I find that trinkets are a little more situational. On the tank, you certainly want to have those defense trinkets available when a healer dies, or when you are tanking more than one mob.
On my rogue, I like to have my trinkets available when I need burst damage. Prince Malchezzar is a good example – if I used my trinkets in Phase 1 they might not be available when we want to burn him down in Phase 2.
So rather than using a whenever-they-are-up macro, I use a visual cue as a reminder, I have my two trinkets on their own toolbar very near the center of the screen.
The two trinket slots on your character sheet are slots #13 and 14. That’s important to know, because when you write your macros if you refer to them as 13 and 14 then the macros will use whatever trinket you have equipped in those slots. That was you don’t have to change your macro every time you switch trinkets.
First, I make two macros – Trinket1 and Trinket2. The Trinket1 macro says only this
#show 13 #showtooltip 13 /use 13
And the Trinket2 macros says
#show 14 #showtooltip 14 /use 14
I use Dominos for my bars. I create a bar that has only two spots. I move it so that it is just off the center of the screen. The two macros are moved into that bar. I hotkey them with Dominos to easily accessible keyboard buttons.
They show a picture of whatever trinket I have equipped in slots 13 and 14.
The add-on OmniCC puts a nice timer right on the button so that it is easy to see when they are available. They make a little “flash” when they become ready, so it’s eye-catching. By placing it near the middle of my field of view, I can easily tell when each trinket is available and use them as needed.