The way people look at you can give you a big insight into what level of attention they are paying you as you speak with them.
When speaking with someone take note of the level their eye lids are at. The position the eye lids are at are a strong indication as to whether they are interested in what you have to say, are shocked or indeed are bored with your comments.
Take a look at the image below:
Imagine for a moment that the blue line is the person's eye lids.
You are in a meeting and discussing a project/sales pitch with a potential client. You feel the meeting is going well and that they seem impressed by what you have to say.
Take a look at the level their eye lids are at. Are they above the Iris? (the coloured part of the eye). If so, this is a strong indication that they are surprised/shocked by a comment you have just made. Perhaps you told them your product can save them thousands a year implementing one thing or another. If they look surprised/shocked perhaps it would be worthwhile emphasising and backing up what you have just told them.
Hopefully you did a good job by giving them more information on your comments. If they are interested in what else you have to say, their eye lid level may well drop to the High Interest state as you can see in the diagram below.
This is a good indication they are listening intently to your comments and that you are interacting well. Of course you cannot take this body signal literally, you have to observe their other body languages too. It's pretty hard to determine what level a person's eye lids are at on a normal interaction, let alone in a business meeting. Are they sitting forward? Do they have open body language gestures symbolising willingness and openness?
All these things have to be taken into account when assessing one's body language. So keep an eye out for it.
Of course if you notice the eye lids starting to close over, its time to try something drastic to get hem interested again, before they fall off to sleep!
Next, go get a mirror and look at the corner of your eye nearest your nose. Either eye, it doesn't matter but notice the part closest your nose. Look out for the red triangular shape that is sometimes visible there. This part of the eye is called the Inner Canthus. If you can see this when talking with someone it is a good indication they are showing a strong degree of interest. If it is covered it is a good sign the person is showing concern or disagreement.
Take a look at the pupils. Are they small or are they big? If the pupils are dilated (big) this is a good indication of interest or excitement to what they are hearing, feeling or seeing. Note however, if you are in a poorly lit room this will make the pupils dilate!
If the pupils are small it could be an indication of lack of interest or concern with what they had seen or heard. Try to go over again what you have said to see if you can regain their interest.
Related: Eye movements, Eye rubbing