If I ever start a hardware company

.. I won't. I'm certain I won't. tl;dr, this just a rant of a whole lot of glaringly obvious mistakes we've made at the two product companies I've worked at.

Hardware is hard because:

• there's no version control. You can't go back in time to checkout what's changed since it was last working yesterday night.
• it takes time to fail. It's hard to simulate time. Imagine testing a battery - you really can't do anything but wait for it to run it's course through time to see if it works in the long run.

And also because your work place always looks like this.

But if an idea comes up that motivates me enough to do it, here's a list of things to take care of. These are actually pretty obvious in hindsight, it's hard to see how I've seen companies mess it up, twice.

All this assumes you have a market already, and the problem isn't acquiring customers, but figuring the tech out. For most companies, I'd argue the problem is the other way around.

• First time right is a myth
  Anything you will ever create will never be perfect in its first iteration. So, you don't try to make the most compact, feature-full hardware tech spec to sell your product at a premium. Attempting first time right is a recipe for failure.
• Design Review
  Review, review, re-review. Just please do review a whole lot. Once you give the green signal to fabricate boards, it takes months to re-fabricate.
• Space Constraints
  Don't bother if your finished product is bigger than you're hoping it'd be because your hardware is taking space. Make it big enough to make things easy to work with, but still something you can sell with the promise of a future iteration with smaller boards. We're struggling to bring products up because we're fighting space constraints. 
• Plastic vs Metal; keep your antenna out of the housing
  Metal housings are cheaper to make. Plastic is expensive. Your antenna can't be inside the metal housing, because duh. If you don't have the luxury of hiring a full-time antenna design engineer, don't struggle with a hundred different antennas, or a tiny plastic patch somewhere on the metal housing for the antenna to radiate. Won't work. Just put the antenna outside. Sell it as a premium product with the antenna inside once you have the money to hire someone to do the antenna design.
• Make debugging easy
  Development slows down a whole lot because we can't debug from the power connector. If you have to open your unit, again and again, to debug what's going wrong, you're wasting time and damaging the hardware with every open-close cycle.
• Protect your circuits, duh
  Power surge protection and reverse polarity. Pretty obvious?
• First sell the ugly-but-works product, then make the compact-premium product
  Make enough $$ by having a fallback and later further investing money in improving the product by making it super-shiny-and-oh-so-very-small.
  Demo it, sell it enough to know common problems during production, and then go for newer designs.