Playing a lot is key but you have to do it the right way. In Malcolm Gladwell's book "Outliers" the idea of "deliberate practice" is discussed.
Basically if you just keep doing what you have always done then you won't improve even if you play a lot. You have to deliberately seek out parts of your game that you need to improve, figure out what you need to do to get the improvement, and then every time that you play focus on improving that weakness.
Just to clarify, Gladwell never actually mentions poker but the ideas in the book are helpful for anyone seeking to improve in any field.
Of course study is important too. Everyone has different learning styles, I personally have gained the most from reading Ed Miller's stuff and joining a video training site. Forums like this one are a great help too.
Good luck