Your muscles in your hand need more excercise. they hold the pencil/pen and having better control over them will help you write faster and neater. Also, practice. Sometimes just practicing writing a few sentences faster and faster a few times will help too.

You can write beautifully, too, if you’re willing to take the time to practice.There are several causes for slow handwriting, including learning disabilities, hand fatigue, poor posture, immature pencil grasp, incorrect paper positioning and bad habits also contribute to slow handwriting. Watch your posture! Try to keep your wrist straight and “hovering” as you write. Make sure it’s not resting on the table. Also don’t lean down too much. Experiment with size and slant. Find a writing style that feels comfortable and looks good.Don’t grip too hard,a soft plastic pencil grip on the end of his pencil is necessary so that the hold of the pencil does not slip during writing and forms a guide for his fingers in the proper position. Keep the letters a consistent size and use a stopwatch for challenge to complete one line of writing in a certain period of time.Practise this for 30 min daily to improve on your speed.

If you just want to take notes in class or something you could learn shorthand.

Practice. practice and yet more practice