when thinking about what route to take on the skilltre you probably need to think about what style you like playing (steady maintenance of mostly predictable damage or gambling on staying out of trouble, typically through evasion by mechanics or kiting as two examples).
also, you probably should have a basic understanding of what each type of defence does.
there are 6 ways of defending your character;
armour - mitigates physical damage
energy shield - acts as a buffer to absorb some damage before it's applied to life (chaos damage goes straight through ES)
evasion - rolled against accuracy, if successful opponent misses. spells can't be evaded.
dodge - applied before evasion, only possible through acrobatics keystone - phase acrobatics applies 20% chance for spells to miss.
block - rolls a chance to avoid taking damage, if the attack would have stunned you a block animation is played which locks you in place briefly.
resists - mitigate elemental damage on hit
these are applied as follows: http://en.pathofexilewiki.com/wiki/Hit_Damage_Calculation
1) Avoiding the hit:
At this stage there is a chance to evade attacks (Accuracy vs. Evasion)
Any chance to dodge from Acrobatics or Phase Acrobatics is also checked here
2) Avoiding the damage:
Blocking is checked
3) Mitigating the damage:
Physical damage reduction and Resistances are applied
4) Taking the damage:
Non-chaos damage is removed from Energy Shield until it's depleted
Any remaining damage (including all chaos) is removed from Life
bearing the above in mind you can then start to think about what will be useful to your play-style and therefore also what gear to be picking up.
for example in Lou's post above he suggested taking the iron reflexes keystone which is brilliant for allowing you gear flexibility and stacking large amounts of armour. but by removing evasion totally you'd need to be aware that you're removing a chance to not be hit. and therefore either focus on ES and armour or keep it simple and go straight for armour only with high resists and possibly a shield for block, bearing in mind the block stun mechanics.
Edited by shamblemonkee at 23:54:50 26-01-2013