You will always feel like you haven't done as much as you wish you would. I'm just starting to accept that, after 6 years of making plans and not getting them all done! I feel like I have a year's worth of ideas that I want to cram into 6 months.
Learning to prioritise is the main thing. At the start of each month I list what I'd like to do. Then as time goes on, each week and each day I prioritise on what has to get done.
I've learned that my actual making part of the day is usually only about 3 hours, at most 5. Not the 8 hours of amazing productivity I initially envisioned. The rest of the time is spent photographing, packaging, mailing, promoting, etc.
What has worked for me is giving myself a dollar amount goal for what I need to do, rather than an unrealistic list of neverending things. I know I can make at least $100 worth of product each day, so if I create that much, then I feel like I have been productive. Doesn't always work when I feel extra overwhelmed, but eventually we need to master the ability to let those feelings go. I'll let you know when I've worked out how. XD