Improving your skills...and learning new things...and developing and growing in your craft sometimes comes from practicing and doing actual work in your field over and over again... until something new brakes open... or a new plateau is reached.
Free is a great way to start out. It gets you jobs, and client relationships, and practice, and the challenging images to learn and grow. What you learn while you are doing FREE...if you are a lifelong learner...will become part of your experience.
Experience is something you can charge for...if you keep a learning head on along the way! You work for free...as a lover...as an amateur...until you gain the experience and confidence to begin charging...then you charge because you are GOOD... and have relevant and valuable experience to offer. Yes, Free is OK. Sometimes its part of being an apprentice...or of paying your dues... to eventually excel at your craft.