The Green pea......somtimes known as the Pitsford pea.
You won't find a more deadly fly, especially early season and it's a doddle to tye.
Standard lure or strong wet fly hook (kamasan B830 or B175's are both good) Size 6 - 12.
Black thread
Black Marabou
Chartause Chenille (lime green...ish!!)
Tye in the black thread at the eye.
Run touching turns to the bend
Tye in a large pinch of black marabou for the tail.
Use the excess marabou pointing towards the eye to form a body. Just run the thread over and over it until you have a reasonable body formed. Doesn't matter if it looks a little scruffy.
Around 3/4 of the way uo the shank, tye in 3' of the chenille pointing back towards the bend. (strip the outer coating off a short length, 3-4mm, and tye this in. this stops the head getting too bulky). Wind 2-3 turns of the chenille up towards the eye. Tye this off and finish the fly off with a black head. It should look like a 'green pea' on a hook with a black body and a black tail.
Add a gold head when you get more confident and a leaded underbody is also a usefull addition. This is also deadly with a white body & tail.
Good luck and i hope this all makes sense!!