Skipping turns is a feature that wasn't added to the series until FFVI. You can't skip turns in any version of FFIV. You just have to Defend and hope that character gets his/her turn again soon, or if it's a battle where you currently have the healer's turn and you know you're soon going to get hit by a strong attack (such as the final battle), you can wait until the enemy does that attack and then tell your healer to use a Cure spell.