There's no rule of thumb for overview settings but the best practice is to separate each type of target into it's own tab. I have it set up that war targets appear in every tab.

This is how i have mine set up:

Default Tab

Hostiles Tab - anything that is a player character and is neutral or below to me goes in here.

Friendlies Tab - players from my alliance, corporation, and fleet show up in here.

NPC Tab - Mission enemies and rats appear in this tab

Objects Tab - I use this section for mission non-collidable objects, star bases, and star gates.