Say your piece and allow your partner to respond. Deliver criticism as soon as possible. That's when it has its greatest effect. Don't store and use it as a weapon when angry. Never criticize your partner in public.
Criticism has different meanings, depending on the setting.
A safe, private space is best. Keep your criticism in perspective. See the big picture, and your partner as a whole person. Criticism is an opportunity. Use it to build trust and honest communication.