How do you get to Carnegie Hall?
Practice. When you think you've practiced enough, practice some more. Then, after you're utterly sick of seeing cards either on your computer or your kitchen table, practice again.
The first time I attempted to count cards at the table, I lost the count after a couple of hands. As it happened, I wound up winning a few dollars anyway, but I knew that all the hours I had spent at home practicing weren't enough. So, I practiced some more. And then, I practiced some more again. Finally, I got it right.
It's like learning to ride a bicycle. You'll probably wreck and you may bruise your knees and elbows, but if you stick with it, you'll eventually get the hang of it and once you do, you'll never forget.