You're talking about starting out as a Warlock and slow grinding speed, that makes no sense. Warlocks are by far the strongest grinding class for the first 10 levels thanks to the amazing Imp and they are as good or better than Hunters after 10 as well.
Fighting multiple enemies at the same time with your imp just comes naturally, you're obviously going to switch to a new target once your initial target has low life and dots on it (or the imp finishing it off).
If you level Alchemy you don't really need First Aid. Always having a Troll's Blood potion on you and plenty of other potions available allows you to grind without downtime.
