Thanking students for their wonderful efforts is always a great way to build morale in the classroom.
Improvement is incremental. And students improve in different ways. For example, improvement might take loner for some students. Regardless, it is important to celebrate success even if it is small leaps.
Be creative and have classroom rewards. You might print of a copy of the following and laminate the certificate. You could assign an award once a week, or once a fortnight. Perhaps, you could assign a bigger award at the end of the term. Individual classroom rewards allow students to see that you have been paying attention to their progress.
Elsewhere you could create provide a book to the student who has shown they can read consistently. Or a brand new notebook (Nothing generic) for students who write consistently and of a high standard. Whatever the prize is, ensure that it is related to your subject in some way.
However, prizes do not have to be extravagant. The odd chocolate for effort is always a great tool to motivate students when they are lethargic and distracted.