The Warlock Buddy is a popular tool that is used by many servers.
As a warlock , open your quick spell menu, and look for the small icon to the right of it.
Click that and a new set of icons will appear (usually on the bottom right of your screen) that allows any Warlock Invocations you posess to automatically apply and keep being applied as they expire.
You generally need to be out of combat for most of them to reapply, although Hideous Blow will keep resetting once per round in combat.
It is highly recommended to use this feature if playing a warlock, especially if you use Hideous Blow.