There are many free worksheets available, especially online, but still the best worksheet is one that you personally draft. This way, you are able to match the level of difficulty of the activity in accordance to the performance level of your own students. It is not bad to reuse worksheets for another batch of students, but once in a while it is also better to vary the activities you give to kids. Worksheets can be made for fun if it is attuned to the current interests of kids. The kids will respond better to activities close to their own interests.
Remember that kids put more attention on animation. They are more interested on having fun so it is best for a teacher to teach them write letters in a fun way. Teachers may have noticed that when children are just being told on what to do, they may not do it right out of lack of interest. Remember that with the so many worksheets available, choose one that is best suited for a certain lesson. Plan ahead what type of worksheet to use for a given day, depending on what you plan to teach.