I've spent most of my sailing career at the helm of various boats. But I've also spent a lot of time as crew. Over the years, I've developed a sense of what I would like to see in new crew. Importantly, I see this in several parts. It takes a long time to develop sailing skills. One skipper I sailed for said it typically took 2 years or more to become an adequate foredeck crew. But knowing the specifics of a position on a boat is only part of the job. Observation and communication are equally or even more important.  So, how do you start out as green, fresh crew and make sure you get invited back?

Learn to observe and communicate. The most important factor in winning a sailboat race is being faster than the competition. So knowing how your boat is faring compared to the competitors is vital. As crew, you can help with this: ask which boats are the competition. Keep an eye on them. As new crew, you're not going to have much to do except move from one side to the other and pull the occasional line. This is because you don't know how (yet). So pay attention to what you are being asked and you will eventually learn the techniques.

Once you know which boats are the competition, keep an eye on them. There are several things to look for:

• Are they changing something? Look to see if they are changing direction (tacking or gybing) or are about too. Look for crew movement on their boat. Fast boats have little or no movement of the crew so if they are moving around, they're changing something.
• Are they going faster than you? The easiest way to determine this is by looking past them to the shore. If you are going faster you will actually see trees and shore features appear in front of their bow (called "making trees"). If your speed is the same, then they will slowly eat trees as both of you move forward. If tress or shore features are disappearing quickly, they are faster than you.
• Are they pointing higher or lower? If you are on the same course, then you should be traveling roughly parallel. If not, then they are doing something different. As a general rule, going upwind, a boat pointing higher (closer to the direction from which the wind is coming) is going to be slower. Pointing lower is faster. Going downwind is the opposite.
  

So having observed any of this, you should communicate it. How, and to whom? Depends on the boat. The skipper has a lot to think about so interrupting that though/decision process too often is a bad idea. Better to find an experienced crew member you can talk to and let them decide if your observations should be shared until you get a good sense of the boat and communication flow. A good skipper will know this is happening at some level even if they're ignoring it at the moment.