I'll put knots into categories:
Must Know
Improved Clinch
Surgeons Knot
Should Know
Nail Knot
Perfection Loop
Blood Knot
Arbor Knot
As you've already figured out, many folks who fly fish like to tell you what's best and how much they know, but our recommendation is to avoid them and go fishing instead. Concerning the knots, we know that not everyone one will agree, but our combined 98 years of experience determined the list above.
The "Must Know" category means you can go fly fishing a bit with knowing these only. For instance, my wife only knows the Must's, but then she always fishes with me and I know all the Should's! In any case, we'll describe each knot and it's usage, and provide a link for you to learn the knot for yourself.
Improved Clinch Knot
The "Clinch" is the essential knot to attach your fly to the leader or tippet. If someone tells you there's something better, you're in for trouble.
Surgeon's Knot
The Surgeon's Knot, sometimes called the "Double Surgeon's) is for attaching two similar (in diameter) materials, like adding some tippet to your leader. It's simple and quick.
Nail Knot
We use this to put a leader on the fly line and to attach the backing to the fly line. There's a tool which we use to tie this knot flawlessly and quickly and you buy the knot tool here.
Perfection Loop
This is also used to connect the flyline and leader. Some fly lines and some leaders are manufactured with these loops pre-tied, but they'll come a time when you need to make your own Perfection Knot.
Blood Knot
The Blood Knot is also used to attached leaders and tippet, and for folks that like to tie their own leaders because it will make a straighter leader that will the Surgeon's Loop. This is a very strong knot and takes some practice in order to tie quickly and accurately. The more you use this knot, the more you'll learn to like it.
Arbor Knot
We use this knot for attaching the backing to the arbor of our reel. This is the simplest knot of the group and you won't use it too often, but you will need it!
Arbor Knot (Canadian Jam Knot) Tying
Pass the fishing line round the arbor. With the free end, tie an overhand knot around the line. Then tie a second overhand knot in the free end to act as a stopper. Finally, slide the knots down tight against the arbor.
Arbor Knot Details
Uses: The Arbor Knot is used to attach the fishing line to the "Arbor" or "Spool Center". In fact the Arbor Knot is really based on a noose knot and, therefore, pulling tightens it. The same knot is used in Bushcraft under the name Canadian Jam Knot where a light rope, e.g., paracord, is being used to compress a load such as a sleeping bag or is used as the first step in creating a lashing.
Tying it: When the Arbor is accessible, the easiest way to tie the Arbor knot is to create a Noose, drop it on the Arbor and pull it to tighten it. If you make a Slip Knot by mistake it will just pull undone. Alternatively, as shown in the animation, first pass the free end around the Arbor or the load; then use the free end to tie the first overhand knot around the line.
Second Overhand Knot: The extra Overhand Knot in the Tag End is tied close beside the first one. It is essential: as the knot is tightened it snugs down against the Arbor.
Improved Version: Some fishermen wind the loop two or three times around the Arbor before making the first Half Hitch. This increases the friction, which may be useful on a highly polished reel. The direction of these turns is critical. They should be wrapped as though tying a Tensionless Knot: rotating the reel should tighten the wraps.
Advantages: The Arbor (Canadian Jam) Knot) is simple, easily learned and effective.
