If you have the money, community college art classes are where I started. Some art stores, like Daniel Smith, occasionally have life drawing sessions. Several art schools in my area also have open life drawing sessions once or twice a month.
On the cheap/light time investment side of things, I'd suggest books and youtube. A good starting place is 'Drawing on the Right Side of the Brain' by Betty Edwards and its accompanying workbook. Stay away from most books which claim they will teach you a popular style, like books by Chris Hart. Once you have a decent grasp of drawing from observation and working from reference, practice drawing from imagination and make it as accurate as possible.
Other than that, it's just practice. If you draw something new every day for a few years, you will be a pretty decent artist. They say it takes about ten years to master a craft, so don't look at your work in the short term. Keep your early sketches and look at them in terms of improvement over years, because that's what it takes.
Good luck!