When you practice scales, arpeggios, exercises, and pieces, be sure to spend some time playing with the left hand alone. Sometimes the less dominant hand becomes dependent on the lead of the more dominent hand, usually the right. As the right becomes more emphasized, the actions of the left become camouflaged. Once that happens, the left can become sloppy in articulation, but go somewhat unnoticed--and uncorrected. Recall too that in repertoire pieces, the "balance between the hands" very often requires the left to be quieter and to essentially play unobtrusive accompianment while the right hand is featured. There are places where the left hand gets to come into its own, but those times are fairly few. As you progress in the literature, the left hand part become more complex in many pieces, containing interesting voicings, inner lines, counterpoints, lush harmonies, etc. When you get to Chopin's Etudes, be sure to do the "Revolutionary Etude". Although the melody is ostensibly in the right hand, the left hand steals the show in doing all the real work. It would be wonderful training for you.
So in matters of velocity, eveness, proper touch, etc., it's important to put a revealing spotlight on the left hand by forcing it to play alone often so that you can see, hear, analyze and judge its performance, and take remedial action as necessary. That's why hands-alone practice is so valuable for beginner and intermediate pianists especially. In fact, there are instances where advanced pianists can better deal with a nettlesome spot in a piece by hands-alone practice. It helps to sort out the details and to better coordinate the parts played by the two hands.
Topic: How do i strenghthen my left hand?