Don't macro Disable. You'll end up wasting it because the target will finish its cast bar before your Disable applies.

Without macro:
  1. You start casting xx spell.
  2. Echidna starts casting Sickle Strike.
  3. You push your Disable button.
  4. You finish casting xx spell.
  5. Echidna is afflicted with Disable.
  6. Echidna finishes casting Sickle Strike.
  7. Sickle Strike hits and does reduced damage.

With macro:
  1. You start casting xx spell.
  2. Echidna starts casting Sickle Strike.
  3. You push your Disable button.
  4. You finish casting xx spell.
  5. Echidna finishes casting Sickle Strike.
  6. Sickle Strike hits and does normal damage.
-or-
  1. You start casting xx spell.
  2. Echidna starts casting Sickle Strike.
  3. You finish casting xx spell.
  4. You push your Disable button.
  5. Echidna finishes casting Sickle Strike.
  6. Echidna is afflicted with Disable.
  7. Sickle Strike hits and does normal damage.

The syntax for an action macro is
Code:
/ac "Ability Name" <target_tag>
/micon "Ability Name"
Where "Ability Name" must have a starting quote, and the capitalization and spacing must match the ability's name exactly. Alternatively, you can use an auto-translate phrase without quotes.
And where target_tag is t for target; f for focus target; 2 for party member 2; attack1 for the enemy marked Target to Attack 1; etc.