Fighting 2 or 3 targets all at once:
Your Felguard in fact can settle them all. Don't make any move before you manually send and control your Felguard to attack your targets one after another. Make sure the Felguard fights every single target for a while in order to control the Aggro of the crowd. Gather your targets by manipulating the Felguard, he will automatically cleave and further stabilize the control. Note that Health Funnel needs to ensure the life of your Felguard. When spreaded targets become gathered, they will be easily settled.
Bear in mind that Health funnel also brings about Aggro of overall targets. Sometimes your targets turn to come at you, you need to stop all actions and have your Felguard re-establish the Aggro control.
Some of your skills are of mass damage- shadow cleave, demon charge and immolation aura. Make sure all the targets are around, Metamorphosis Demon charge will stun the targets, Shadow Cleave and passive Immolation Aura together will create powerful AOE which kill targets within a short period of time.
What if I am no match for an Elite mob?
Solo in the wild may be extremely brutal for a warlock despite his/her ability to beat most of the Elite mobs. Felguard/Voidwalker can still be used to defend against the attack when facing an overwhelming mob. Here these companions have to made sacrifices so that you gain enough time to leave combat asap. These mobs usually move at the same speed as yours, so as long as you keep appropriate distance from them, get away from them won't be a problem.
Under the circumstances where you are facing more than several powerful mobs' attack and it's already been beyond your ability to control their Aggro by manipulating the Demon pet, a soulstone self-bound is indispensable. Move yourself towards a safe area of main road, uphill slope or river. These sorts of areas will make sure a warlock securely survives with a souldstone when mobs believe their target is dead and go back to patrol.
Fear or Howl of Terror are also smart skills employed to gain time and leave a combat. However, warlock players need to be very careful using this strategy because a feared mob most probably will bring other patrolling mobs around its path.