Understanding Leader Usage

I've been on a leader kick lately because I am very cautious about my leaders when I am guiding. However, this year I have lost several fish due to getting lazy when I am fishing for myself. Bad knots, frays, short tippets, or wind knots can spell disaster. Problems with leaders can cause a lot of stress for you. The wrong leader in the wrong situation can make it difficult to be successful. With that said I wanted to post an ABBREVIATED guide to understanding leaders.
I find the best way to make sure all goes as planned is to fish new, out of the package tapered leaders but for those of us who fish a lot that may not be practical. I build my own leaders but a lot can go wrong doing things that way and a leader formula that works for me may not work for you or a formula that works in some situations may not work well in others.
Its no secret that fish in pressured areas or clear water can become leader shy. With that said using a leader the right length and size is paramount but you don't want it too long and you don't want it too light, its a fine line.
The benefit to making your own leaders for me is cost, in addition to that I can adjust a single leader to adapt to any fishing situation I encounter rather quickly. But in the end, the key to understanding leaders and ensuring they work is to understand diameter and knots.
Even when working with tapered leaders tippet length and diameter are what you need to be focused on. I have recently switched form Orvis leaders to Rio but they are generally the same thing. If you take a nine foot 5X leader you are getting a leader larger in the butt section that tapers down to a roughly 20 inch section of tippet that is somewhere in the neighborhood of .150mm in diameter.
The next piece of information is what we need to focus on. In order to ensure that any knots you tie, whether to extend the length of the tippet or replace a broken section be tied well using a piece of tippet  that is equal to or close to the diameter of the original tippet. Too many anglers tie on a piece of tippet that is too small in diameter compared to the attachment piece. This makes for weaker knots that do not bind as well and can sometimes create significant hinge points that hinder the ability of the leader to turn over the fly.
Keeping that in mind when you build your own leaders you need to make sure as you taper your leader down using good strong knots, make sure the pieces you are attaching don't differ too greatly in diameter.
As far as knots go, in my opinion there is only one choice, the blood knot. The blood knot holds very well and when tied correctly should not fail unless you strain the line too much on your end. With practice the blood knot is easy to tie but in my opinion too many anglers shortcut this knot by using a double cinch knot which although similar,  is not quite as good. I will share a basic formula or two from Jason Borger for your own information but its important to play with these formula's yourself to better match your fishing and casting style.
The other thing to remember that I touched on briefly before is to regularly check the condition of your leaders. Check for knots, fray, discoloration and length on a regular basis. A break due to neglect will ruin a memorable fishing experience rather quickly.