Use motivational stickers freely. The cost is minimal. Students take great delight in amassing collections of these, however. Praise the student in front of other teachers as well as in front of student's peers. Students feel a greater sense of accomplishment when they realize that their performance was worth sharing with others, especially other educators.
Quantity is just as important as quality.
Students need consistent affirmation. Students will recognize and resent insincere flattery. Praise especially after correction. This assures the student you still value him or her as a person and believe he or she has great potential even when a mistake has been made. Teach students to praise one another.