In fact, you can criticize and compliment at the same time using the "sandwich approach" where you take the thing you want to criticize and wrap it around two compliments.
Here's an example:
Stephanie has set a couple of down screens poorly and must be corrected. Here is some great dialogue from the correcting coach.
"Stephanie, you are such an important part of our offense when you set good screens. But your last two down screens you failed to get your back to the ball. Concentrate on getting your back to the ball on each down screen. Our team needs you to screen well for us to be successful."
Stephanie's name was attached to "importance part" in the beginning and "team needs you" in the end with the correction in the middle. It will be much more conducive for her to listen in this manner.
Here are some more thoughts from Maxwell:
Another way to develop confidence is to put a few wins under your belt. Start with building on small successes, and little by little you will tackle bigger and bigger challenges.
Another way to increase your confidence is to quit comparing yourself with others. Comparisons always leave you found wanting.
One of the surest ways to build confidence is to find one thing you’re good at and then specialize until you are special.
A successful leader knows that he helps followers most by helping them discover their special giftedness, encouraging them to develop it, and then disciplining them to use it.
Everyone needs to be affirmed both as a person and as a coworker. It’s easy to give a generic compliment such as “You’re great to work with.” But as comment that really means something is specific and mentions a certain quality: “I appreciate your efficiency in relational skills, and this is very important to the success of the group.” We don’t help others by passing on empty compliments or avoiding the necessary task of sharing needed constructive criticism.