The notion the these “rules” are restrictive is a bit backward. The “rules” are there to guide you, to help you create a form that people will be instinctively attracted to. A bit of reverse engineering, if you will. The grace, beauty, balance were there long before the ‘rules’ were stated.
A few years back I took a pottery class,,where I enjoyed making bowls, no big surprise. After the thrown bowls firm up for a few days, they have to be remounted to the wheel to trim, create a foot from the wider base left by the throwing process. Sound familiar? It’s easier and quicker in clay. At the time, I wasn’t aware of the thirds rule about foot size. So, I trimmed them to what looked right to me. Then I learned the rule, a bit late. So, I measured all of what I had made, rim size to foot size. Wouldn’t you know it? Every bowl had a foot that was 1/3 the rim size + or - 3percent.
What I saw when I was working was that larger than that looked clunky,,less seemed unstable.
So, what I would tell someone starting out, someone who hadn’t developed their ‘eye’, would be make the foot 1/3. This will put you on your way to a form that will be more balanced as viewed by most anyone, with or without design experience.
@Curt Fuller above states that he stays away from rules, but looking at his work which is all very lovely, I see really nice forms, can see that they come from one artist,,one view, one hand. And I’ll bet if one measured them we would find that they fall right in line with these design rules. Curt’s ‘eye’ is developed, by whatever means or path, not necessarily by reading the ’rules’, but by observing the rules in nature, in beauty around him and all of us.
We mostly all know a beautiful face when we see one, right? A pretty woman is just that, the world over. Would knowing that there is a mathematical formula to that beauty ruin it for you? Hopefully not. But if you wanted to learn to draw a pretty face, you would put yourself ahead by learning facial proportions.
With your designs and projects, you should just make whatever feels right. But then, take the time to look at it, enjoy it with an eye toward improving on it. Keep at that idea only changing the aspects of it that could be better, again, in your eye, and again only speaking of the design (not sanding or finishing or better tool work). You might be surprised to find the changes bring your design closer to the ‘rules’. Why? Because you’re a human animal.
They aren’t so much ’rules’, as ‘shortcuts‘ to beauty.