Taxi is usually fastest (flat fare $45+tolls+tip) but travel time can be tricky on Friday evenings. You can also take subway/AirTrain ($7.25): walk west on W 4th St (towards Washington Sq) to the A subway station at W 4th & 6th Ave. Take the FAR ROCKAWAY-bound A subway (NOT the Rockaway Park-bound A) to Howard Beach/JFK, transfer to AirTrain to all terminals. Travel time about one hour, so you should be fine if you get to JFK around 6:30 or thereabouts.
Taxi is usually fastest