[Suicide Junkie]

Your ships have a dotted line around them, right? Use the blue-circle & ship icons on the top right of the control panel to cloak/decloak

If any of your ships run out of supplies or otherwise have their cloaks deactivated, the enemy will easily see you.

Also, beware of cloaked enemies with cloak defeating sensors. You can't see them, but they can see you, and therefore their friends can see you too.