Preperation:
resevoir cap off, and diaphragm if there is one
lever level with the ground
caliper orientated to get the bleed nipple as high as possible
ring spanner and clear pipe on the nipple
resevoir 3/4 full
ALWAYS WEAR GLOVES AND EYE PROTECTION!!!!!!!!!!!!!!!!! 3.99 for some halfords goggles Vs brake fluid in the eye doesn't bear thinking about
Now do the folowing
Squeeze lever to put presure in the system
open nipple 1/4 to 1/2 a turn
allow fluid to escape into pipe
close nipple before the lever reaches the bar/limit stop, impractical untill its at least partialy bled i know, but more important once most of the air is gone. Never release the lever with the nipple open.
Close nipple
Release lever slowly (or you'll get a face full of brake fluid as it squirts back into the resevoir)
Check resevoir level, top up if nececary
Repeat the process untill fresh fluid is coming through with no air in it.
You are using shimano mineral oil arent you, not dot3/4/5.1 fluid which will ruin the seals?