From the character config screen, select the "Target Filters" tab. At the top of the list, you'll see one for "Weapon Sheathed" and another for "Weapon Drawn." There are additional customizable filters available here as well, but for now, let's just talk about these two. As stated earlier, if you're on a job who never has a need to target another PC during a battle, the "Enemies" filter is just fine for "Weapon Drawn." If you're on a mage job, you might want to re-assign the "Friends" filter to that position. You can even modify it to include NPCs and such.

With this done, you'll discover these things: you can now exclusively cycle mobs via the tab key(or the trigger combo mentioned above) and still target any PC you like using the number pad(or D-pad), whether they're in your party or not.

I know this information might be old news to a lot of folks, but I just wanted to throw it out there for any other newcomers like myself who've yet to discover it.

Hope this helps!