Phil,

To keep things super simple for you, the BEST way to improve your left hand is to practice your scales. You must practice with both hands, all twelve keys, start at 60 bpm or slower until you can navigate the keys and the scale perfectly without making a mistake. Get a hold of a good all around beginner piano book and learn the fingering for the scales. If you practice this 1 hour a day, you will improve your fingering and synchronization of both hands dramatically.
Don't be discouraged if it doesn't happen in 2, 3, or even 8 months. You have to have the mindset that keyboard playing is for the long haul. If you want to get up to speed quickly, then you must practice your scales 4-6 hours a day (this was quoted from my teacher!).

Good Luck and Have Fun
Al