Well most veteran CHs agree that /tellpet is a nice addition to the game....lord knows we were running out of creative commands to teach our pets. You can only hear "a" spammed over and over so many times before you pull your hair out. Regardless there are still many people out there who do not take advantage of it. So for those who may not know just how to use it, or how to set up macros for your pets....I've made this little run through.
First thing you need to do is train your pet in all the given commands that you have. Once you've done that make a macro that uses /tellpet to issue the command. For instance if your command for your pet to attack is "Kill" just open the new macro box and type in "/tellpet Kill". Make sure to get the capitalization right as /tellpet is case sensitive, that means if you use "/tellpet kill" it will not work.
After you have a macro set up for every one of your pets, go into the Options panel and go down to Controls. From there open up your Keymap (bottom button in the Controls), and locate the Custom tab. There you'll find every one of your macros that you've made so far. To bind a macro to a key simply double click on the macro's name, then push the key you wish to use. Personally I use the NUMPAD since it's easy to get to, and I don't use it for anything else. You can also use combinations of keys, for instance Shift+NUMPAD5, or even Ctrl+Shift+NUMPAD5.
This is how I have my bindings set...This is just a basic of idea of how you can set your's up, there's a lot of room to add on there. You could potentially add every pet command you are able to train to the NUMPAD using the Shift+, Crtl+, or Alt+ combinations. You are by no means limited to only using the NUMPAD to bind your macros, but I find it's the easiest way since the keys are clustered and there's not much use other than camera movement (which I myself don't use).
Hopefully this helped a few people out, and maybe it will cut down on the spamming of "f" and "a"