The formulas that I present here have been proven and have served me well for many years. You will need a selection of tapered leaders of 6 ft. to 12 ft. in sizes 2x-8x depending on the type of fishing you do. The shorter 6 foot leader will be easier to cast but the 9 foot leader is recommended if you can handle it.
There is no consensus among fly fishermen whether beginners are better off with knotless or knotted leaders except that the knots catches algea, advantage is that it is better to have the algea on your knots than on the fly. Most manufactured leaders are knotless, whereas those who use knotted leaders generally construct them themselves.

As a preference, I tie my own with Maxima (Meinel KG). The knots really dont make a difference. The heavy sizes are quite stiff and the lower sizes are very limp and that is what you are looking for in leader material. Dont get fooled by bying cheap mono. They are not worth the price!
I use a barrel knot to attach them to each other.
I use the needle knot to attach the butt section to the fly line which is about 45cm (18").
With this short piece of butt mono you wont have to re-do the needle knot every time you want to change your leader. All you'll need is a barrel knot to attach the leader to the butt section. This piece of 45cm (18") wont be included in the lenght of your leader, it's just an extention of you fly line.

You will have to add about 4cm (1.5") to each sections that you use so that the lenght desired will be accurate. The knot will take the extra 4cm (1.5") when you tie them to each other.

Leaders have a "tippet" section which is at the end of the leader where you tie your fly. The tippet is always of soft mono, two feet long. As this tippet is used up, it can be replaced by tying a new piece of tippet to the end of the knotted tapered leader using a barrel knot.

Tight Lines