Do not go for extended trades against Irelia as her Passive will fully proc when 5 spells have been used. You will not out trade Irelia without a clear advantage like health or mana.
Be careful when standing near low health minions as Irelia will look to use her on them to close the gap and skirmish with you. She might even look to herself and then get on top of you and stun you with her .
When Irelia tries to use her on the minion wave to last hit, it is a potential opening for you to poke her as she cannot dodge your spells while moving in her animation. If you have CC or skill shots, throw them in the direction of her minion so she gets hit with them.
Watch out for Irelia in teamfights as she will look to flank your team. Try to take long team fights through pole and stay close to one another and limit time spent isolated.
Irelia will look to split push whenever no team fight is occurring and she will always try to catch the enemy off guard when they try to stop her. Do not let her push for free, but at the same time do not over extend without backup.
Try to kill Irelia’s carries before a team fight starts or at the beginning of a fight as it will severely reduce her and her teams chances of coming out ahead.
Irelia peaks during lane when she has 5 stacks on her Passive because she gains bonus attack speed and damage. Do not fight her when she has near-max stacks as she will always out damage you.
Avoid trading with Irelia at level 1 as she might try to engage on you at level 2 and shut you down. This is especially true if she has Ignite as it will deal extra damage and increase her kill potential in lane.
Irelia gains a small spike once she has Tiamat as it increases her trading potential as well as wave clear. Do not go for extended trades as this item will bring her out ahead.