...I seem to do very well against standard foes, but horribly wrong against bosses and dragons... anything I should know?
In Light Armour, you must remember to
move! Dodge, faint, sidestep, strafe, in and out. You are not a tank and must use your abilities to your advantage.
Trading blows is not your goal. Instead, get in your shots and get out before they respond.
A useful tactic I've found for melee combat in Light Armour: Use a torch as your shield.
You can block with a torch, and bashing with one will set your foe on fire.
Enemies on fire will then take additional damage when struck with your melee weapon.
Highly satisfying to torch-bash a Troll or Spriggan, whackwhack with my 1H axe, back pedal and strafe left, re-engage with another torch bash/axe chop combo and repeat.
That torch bash, as with any shield block, will interrupt their attack allowing you to get in one or two good shots before disengaging.
Get in, inflict unexpected fire+melee damage, then get out.
Works wonders.