How fast can they run compared to (most of) the PCs? If more than 2-3 PCs are high-mobility characters such as monks or rogues, the drow may have difficulty disengaging.
Have the drow skirmishers consist of rogues and monks who will use bonus-action Dash and/or high natural speed to quickly disengage, and have them attack from hard-to-reach positions such as clifftops or tree platforms.
Have each squad split into two groups. One advances to within 60 feet of the PCs so that they can open with faerie fire and then get in a round of sniping with sleep-poisoned bolts. The other hides 60 feet further back, and will either cover the first group's retreat using darkness or, if the party splits up to pursue the first group, will circle around to try and sneak attack the smallest or slowest sub-group.
If this is their native territory, don't be shy of giving them a few well-placed traps and hazards to slow pursuit.
Don't make them too perfect - let at least some get caught out of cover as they retreat - and if they take more than one or two casualties, let them retreat to regroup, allowing the PCs time to rest and heal up.