I know there is a lot of info out there on the internet but since this is a carp forum and we do not have a post about this yet...I also posted this on Mafishfinder.com but since the forums are separate I figured I'd repost in the 3 places I fish/visit most.
The hair rig is a very good and versatile rig for carp fishing, especially in waters where carp have become wary of hooks. I am going to show you the basic method but by no means is it the end, there are plenty of modifications that can be tweaked to suit specific waters and habits.
Step One: Gather materials.
A few things about this picture, I am using sponge to represent the bait so I do not have to actually use bait atm. Also the baiting needle can be made out of a straightened hook, or my favorite is using a sewing needle, cut one side of the eye then put the pointy end in a small dowel or wrapped in tape or what not. For this demo I am using a soft braid line for my lead material and size 4 straight shank hooks.
Step Two: cut off a section of line, about 18 inches to make sure you have enough room to work with and tie a small loop in it.
The loop is done by simply doubling over one end and making a basic overhand knot.
Step Three Thread the bait onto the needle and thread the loop on
Step Four: Thread the bait along the needle and onto the line
Step Five: Remove the needle from the loop and use something to stop the bait from sliding off. These can be small plastic dumb bells bought from bait shops, small debris like sticks or grass, pieces of rubber bands etc.
Step Six Now we can thread the hook onto our line, taking the line through the eye from behind the hook to front
Step Seven: The reason we put the bait on is to measure the size we want for the bait we will be using. The sponges represent kernels of corn which is a very common bait. We want a small gap between the curve of the hook and the bait, lets say about 1/2 inch. Once we move the hook into position we begin wrapping the line around the shank of the hook and the hair, just below the eye about 6 times. This is the same method for snelling a hook if you are familiar with that.
Step Eight:Now we bring the end of the line back through the eye of the hook, again from back to front and pull it tight.
I also want to include this short video I made that detials the same process which may help as sometimes seeing is better then reading.
And there you have a basic hair rig. This is another example of the hair I have used with much success
What you may notice on this one is I used 1 piece of corn, 1 foam to float it a bit, followed by 2 more pieces of corn. This keeps the bait more neutrally balanced and not just sunk on the bottom, which helps in heavy silt areas or those with a thick green blanket weed.
Anyway I hope this helps, from this basic rig many modifications can be made to suit your particular waters and/or needs. Please feel free to post anything you have found that helps in making these rigs or changes you have made for specific waters etc.