Study from books- that's how you improve. I find video lessons to be helpful too, but with books you can go over the material at a slower pace, studying and playing through the variations to better grasp the concept of the lesson.
Playing longer games (as opposed to blitz) also gives you more time to think, which is more helpful. Blitz skill comes from experience after you've played many long games, as you're pretty much just automatically making moves based on intuition, which comes from experience.
To get better at chess, you have to both study chess and play chess. Studying gives you the knowlege you need; playing games allows you to practice what you've learned. Playing against computers will help you solidify your game and avoid tactical blunders, which will ultimately help you spot your (human) opponent's blunders and take advantage of them.
Oh, one more thing... practice tactics problems!
But that's just my 2 cents... Cheers!
I've actually been thinking about this indirectly (never seen the thread till now).
When you look at the old masters before computer era (who are much stronger than probably anyone posting on this thread still). They were not playing online 24/7...so study-wise, you dont /need/ to be online playing that much (thats my theory anyway).
BigKingBud had intesting post too: "I'm in the last chapter of TAM at the moment, and it has become VERY clear to me, that I need to start playing longer games each day for a while, and completely avoiding the 2 and 10 minute games."
I've had problems otb from playing online blitz. I just dont do it now. Dont claim any words of wisdom.