What I explain below is the way I do air-layers. It isn't the only way but I find it works for me.
The material in the photos is a narrow leaf Ficus Benjamina.
To start with, select round about where you want your layer to be and find a node near that position. In the first photo you can see where I have removed a small branch - that is a very suitable place for the layer.
Next, with a very sharp knife (stanley or similar) and just below the node, push the blade into the bark till you feel a lot of resistance. Don't saw at the bark, push the edge of the blade in. When you come up against that resistance, and keeping the pressure on the blade, slide it right round the trunk to where you started. Do the same about 3 cm further down the trunk. You now have two rings round the trunk. Do one cut from the top ring to the bottom one and lever the bark off all the way round the branch. It may not come off all in one piece so keep peeling till it is all off - photo 2.
Congratulations - you have now 'ring-barked' your branch or trunk! If you just left it like that, the upper part would die.
The new roots will shoot from the top of the cut section, so put some rooting gel or power all round this area. My preference is one of the gels because it is wet so doesn't draw any moisture from the cut.
Now you need a piece of clear plastic sheet - doesn't matter how thick or thin it is. Cut it wide enough to extend way above and below the ring barked section and long enough to go round the area with plenty of room, then put it round and join it with some tape - gaffa or duct tape cut into strips is fine. Make sure you have enough overlap to be able to seal the join completely - photo 3.
In photo 3 and 4 you can see the ring-bark inside the plastic.
Photo 4 shows where I've used some tape to hold the lower plastic into the trunk - you don't need to do this, you can just wrap a piece of wire round it. I find it easier to put the tape on first though - it hold it in place while you are putting the wire round it.
Now you need some sphagnum moss (available at the B store or nurseries). Sphagnum moss is completely sterile and inert - but don't try eating it - it is toxic so be a bit careful with it. Dip it into some water and gently squeeze out the excess but don't wring it out completely - the new roots need something to drink. Put the moss in the plastic tube you've created and make sure it goes down below and up above your ring-bark and fill the tube with it. Then seal the top the same way you did the bottom - photo 5. Wrap a piece of wire round the top and the bottom and twitch it up as tight as you can without snapping it - photo 6. The whole thing needs to be as watertight as you can get it otherwise you will be continually unwrapping it to add water to the moss - if the moss dries out, your air-layer will die off.
Finally, wrap a piece of black plastic sheet round the whole thing and tie it in place with a nice little bow - that's so you can undo it easily to see how your layer is going. Again, this step isn't mandatory - you can just leave the clear plastic as it is. I do it because my reasoning is that roots grow naturally underground in the dark so I try and replicate that by covering it with the black plastic.
That is now a completed Aerial Layer. All you have to do now is watch it and make sure it doesn't dry out. If you do need to add water because it is leaking somewhere it is better to use a syringe pushed through the clear plastic rather than undoing the layer. Undoing the layer runs the risk of breaking off any new roots that are forming - they are extremely brittle.
When you see the tube is full of new roots - they will be round and fresh as against the sphagnum moss dull creamy colour and flat and ragged - it is then time to remove the layer completely. Have your pot ready with some potting mix in the bottom. Take off the black plastic but leave the clear plastic alone, and if the branch is too thick for a branch cutter or secateurs use a pruning saw and cut just below the bottom wire. Take the wire off the top and the bottom and then remove the tape - be very careful how you handle it now because the roots are extremely fragile and delicate. Cut the clear plastic up the side and take it off. Now, without disturbing the roots or the moss, put the whole thing into your pot and fill with potting mix to above the moss level. At this stage the roots will be a tangled mess, but don't worry about that - they will be sorted out on the next re-pot and root prune. Some may stay tangled but others will venture out into the potting mix - those you will keep, the others will be removed. Dunk the pot into a bucket of water and leave it for an hour or so to completely soak the potting mix. Let it drain then put it into a semi shady position for a couple of weeks to allow the new roots to develop. After about a month it can be put out in spot where it gets a few hours sun per day and a month or so after that it can go out in the full sun.
As I said, this is my way of doing it. Others have their own way. One person I know doesn't use plastic at all. He uses Alfoil. He wraps the alfoil round the trunk to make a cone, fills it with sphagnum moss then seals the top. In our heat up here I don't think I'd like to leave that one out in the sun - I think it might just cook the whole thing.
Different trees take different times to set roots. Figs are relatively quick. Pam had a full rootball on her variegated fig in less than two weeks. Pines can take up to three years to put out new roots, so don't worry if you don't see any roots within a short time, just make sure it stays moist, and if the foliage above the layer is still healthy then everything is fine. I taught my next door neighbour how to apply aerial layers and he has been layering his lemon tree with great results. Even though the original tree is a grafted one, the air layers are growing just fine on their own - we even have one of them growing in our garden and it has already produced some nice lemons.
One of the advantages of air-layering is that if it is a mature tree that sets fruit that you are working on then the planted layer will fruit as well as opposed to using seed that might take up to five years or so to produce its first fruit.
Try it people - but don't use your prize tree for the first couple of attempts just in case.
I think that your style of writing makes it so much easier to visualise as you read (pics make it better, of course). And, it makes sense! 
). I've read and reread your instructions and even printed them off!
