The same is true with writing. Unless you write a little each and every day, you can't expect to see any improvement.
Before I started writing every day, I was unhappy with my prose. I couldn't figure out why parts of it looked so clumsy and unskilled. Once I made a conscious effort to not only read more but to also write at least 500 words each day, I saw drastic results. My writing improved, my confidence soared, and I developed a deeper appreciation for the craft of written language.
How much should you write each day? Honestly, it's up to you. Stephen King pumps out no less than ten pages each day, but that terrifies me, so I aim for 500 words of anything before I go to bed. A lot of beginning authors start with 350 words. Some aim much higher, aspiring for King's lofty standards. Still others write not by word count, but by time. I know writers who set a timer for fifteen or thirty minutes and pound away until the buzzer goes off.
You should choose whichever system works the best for you. The only thing that matters is that you write every day, even when you feel uninspired.
What do you think? How much do you try to write each day?