Spotting the airplane is often a lost art these days. In the old days with round parachutes, a low pass was made and wind drift indicators were flown out and watched to see where they would land. This would help with the more precise spotting needed for rounds which were not very steerable.
In the modern day, we jump highly maneuverable square parachutes with good forward speed. We also have GPS’es which help direct the plane to a precise spot over the ground. We can get back from much worse spots than in the old days, yet people still stand off sometimes. It is often because they just depend on the pilot without even checking the winds on the ground and figuring out where they should be getting out.
If you picture an aerial map of the dz, straight north is a 0 heading, east is 90, south 180, and west 270. Unless you are doing CRW or opening high, you will mainly be concerned with winds at 3k or lower. If you are doing a normal freefall jump, you will be in the winds at 6 for 15-18 seconds, at 9 for 15-18 seconds etc. So unless the upper winds are extremely high, you will only drift so far in the 30-60 seconds of freefall. For example if winds are 20 mph all the way down, 20 miles/1h = 20/60 miles/ 1 minute or 1/3 of a mile in one minute. So there is drift but the effect is amplified under canopy because you will be spending a lot more time under canopy. It is important to note that winds aloft forecasts are usually given in knots, and 1 knot = 1.15 mph.
So if all of the winds are light out of the south, jump run will normally be run to the south, with the first group perhaps getting out a little short so that the last group isn’t too long. The higher the winds, the longer the spot will be to help people avoid getting blown past the drop zone.
So what if the upper winds are a different direction from the ground winds? If for example, the upper winds are out of the west, and the ground winds are out of the south, we might run jump run to the southwest, so that we will drift east in freefall, ajjjnd then open south of the drop zone. Note some drop zones might be long and skinny, and they may choose to run a drop zone straight south but offset to the west, or straight west and offset to the south. This helps if you have a long, skinny drop zone with few outs in the other direction.
What about if the upper winds are opposite of the ground winds? Luckily this doesn’t happen very often because it becomes very tricky. If you fly jump run into the lower winds, you can have an extremely high ground speed on jump run. It is very easy for later groups to exit too far away to make it back. You also have to leave minimal time between groups to help with that problem. If you run the jump run into the uppers, you have to start the exit quite early so that later groups don’t end up short. Especially seeing how later groups are often high pullers under large canopies, having them open near to the drop zone can be problematic.
If you are in charge of the spot, it is helpful to watch out the window on the climb up. If you have an idea of what the normal airplane speed looks like, you can get a reasonable idea of what direction the winds are coming from by noticing whether the groundspeed of the airplane is higher or lower than normal. If you notice that the airplane is pointing north, but moving northwest across the ground, then you know you have a crosswind at that altitude. You can also cheat at this a bit by looking over the pilots shoulder and comparing the groundspeed on the GPS with the airspeed of the plane. This can be helpful as sometimes winds can change during the day.
So once you are on jump run, and have a good idea at what the spot should be, you should be verifying that the pilot is flying jump run on the heading you want and flying over the airport (assuming you are not doing an offset jump run). When the pilot opens the door, stick your head out of the airplane, look out to the wing and then straight down. It is important to not use the airplane as a reference, because if the airplane is climbing or descending, perpendicular to the airplane may not be actually straight down. If you look straight down, and you are short of the spot, you can wait a bit before climbing out. Do keep in mind that if you have 2-4 people climbing out, you can start climbing out a bit early of the spot so the exit doesn’t end up long. (If the GPS is working, you can check the heading and distance by looking at it as you are on jump run.
You also want to be looking for airplanes or other traffic. Its a skydiver’s job to see and avoid. A pilot 5000 feet below you will never see you coming. If the spot is wrong or too far away, it is okay to ask for a go-around or give corrections! Corrections are normally given as degrees right or left - i.e. 10 right or 20 left. The pilot will make it back to the drop zone - you may not! If you realize in freefall that you are a bit long, if circumstances permit, breaking off a bit higher and pulling high can be helpful. But do be aware that if you are out in an early group on a big plane, you don’t want to pull very high because it might cause a freefall/canopy collision with another group.