Summarize this article:

Keep the strength in your hand by writing with it and using it daily.   Allot left handed writing. Perhaps you always write on a calendar, or constantly update a grocery list—assign small tasks like this to your left hand to keep it in use. Practicing your left handed writing daily will keep your cognitive performance at a high level. Continue improving on your left handed writing by beginning to draw.  Begin with very basic shapes: squares, triangles, and circles. Work your way up to more difficult drawings. The more your movements become directed but natural with your left hand, the easier it will be to maintain your left handed writing. Using both your right and left hand improves connection of the left and right brain hemispheres.   If you switch entirely to your writing with your left hand, you will lose writing skills in your right hand. Creativity and abstract thinking have been said to improve when you use both your left and right hand interchangeably.

Summary:
Practice daily. Start to draw. Switch back and forth.