Dear Mariam, When it is with regard to a part of body or illness, you can always use "好些了"- 我的病好些了，我的身体好些了，我的感冒好些了，我的精神好些了。you can understand that we use this expression to describe a change from a "bad" or "negative" situation to a "good" or "possitive" one. But when it with regard to skills, there is no change from "bad" to "good", but from "good" to "better", so we normally do not use 好些了。instead, we use "更"。我更有信心了，我的书写更好了，我的中文更好了。 hopes this might help:) best Biying