make sure you do it when the motor is still warm, all the plugs are out at the same time. remove the intake tube and hold the throttle blade open. a jumper pack on the battery or a battery tender also helps.
if you find a cylinder low, obviously do the squirt a tiny bit of oil test in and retest. if compression comes up, that's rings. also, if one is low, locate and use a leakdown tester (harbor freight, last I checked about $50), or if you don't have one, hook your air compressor line up to the compression test line. you'll need to be a little bit creative and remove the check schrader valve from the compression tester. regulate the line at 100 psi or so.
open oil cap, listen/feel for air coming out. close, then check coolant cap. crack the throttle body, listen. go to exhaust pipe and listen.
where you hear the air coming from, is your problem. out the oil cap is a lower end issue - rings, hole in piston, crushed ring lands, gouge in cylinder wall, etc. out the coolant cap is a head gasket or cracked block into coolant jacket. out the intake is intake valve issue, valve spring, etc. out the exhaust vice versa. but the leakdown tester is a huge advantage.