Writing skills can be a difficult thing for some children to master. Trust me, my youngest is a "lefty" and I struggle helping him hold the pencil correctly. However before your child can learn how to properly write in manuscript/ circle and stick/ ball in stick, he'll need to be able to form basic round circles and control his lines to make them more straight and less squiggly.
Practice making the basic shapes, such as tracing circles and lines and zigzags before you even hand him a sample paper with letters to trace. Then help him "see" how the different shapes work together to form letters. For example, the letter "a" looks like a circle with a stick connected to it on the right.
Read THIS ARTICLE for great information (and resources down below) or check one of the Amazon books or charts geared towards teaching writing.