The Correct Way to Practice

Practice is not just about the time you put in.  It's about the quality of practice you produce.  It's also about repetition and practicing with purpose.
An example that coincides with another sport is Football.  Every summer the NFL starts their training camps.  The players at these camps have played football for 15-30 years.  They're some of the best athletes in the world.  As the teams introduce the playbook, each team conducts walk throughs to start ingraining the movements that each player is responsible for.  As the players become more familiar they start running the plays at regular speed.
This process is no different than working on the golf swing.  You must first know what you're working on, then you must practice it over and over to get the feel.  Going slowly in your practice swings is a good idea.  This allows you to get a feeling of whether you've done it correctly.
Repetition is crucial in implementing improvements in your game.  They can be done with a club or without.  As well, the can be done mentally.  This helps you improve the picture in your mind.   There's no substitute for practice. Practicing correctly gives you an even higher percentage of opportunity to improve.