Does this means a character can generaly avoid taking an opportunity attack by declaring the action as a readied action?
For example, can a ranged character use a ranged attack on a adjacent opponent without taking an attack of opportunity, by declaring the attack as a readied action: "Whenever the opponent taks a minor, move or standard action" ?
That seems a bit gamey and cheap to me. :-/
It really depends on how specific your DM wants you to be in choosing a trigger for the readied action. For example, I don't think it would be too out of line to request that you be more specific than minor/move/standard. A trigger such as "this enemy attacks myself or an ally" would be more in line than simply "takes a standard action."
A few other considerations:
-The readied action is an immediate reaction. If your attack would kill the enemy, you've just let it do it's nastiness anyway. Not much difference if their on-turn attack is the same as their opportunity attack, but if they have conditions/effects/riders to their on-turn attack, then they get the extra opportunity to inflict it upon you & your allies.
-Similarly, if you are inflicting an effect, inflicting it during the enemy's own turn can weaken its effectiveness.
-If your target has allies who can get in melee around you before the target takes the triggering action, your attack will still draw OAs from these other baddies.
Overall, you could ready an action to avoid allowing one creature one chance at an OA, but usually there are much better things you could be doing than attacking in this fashion.
-Dan'L