Two things to consider when first looking at a space: who is going to use it, and what are they going to do there. Spend time really considering this and have a clear picture in your mind.

Customer Experience:
Think about the user experience. We buy Apple products because the user interface is the most intuitive to use. It’s easy to learn, and feels natural. A well designed space should do the same thing. When you enter a space, you should understand the purpose.

Be Thoughtful, Details Matter:
Write out floor plans. They don’t have to be “to scale” but you do need to account for every inch. The devil is always in the details and often a few inches can make or break a decision. Make sure windows are centered. Trim, knobs, fixtures all must match. People notice when they don’t.
And one “off” thing has a psychological effect. Like a thread that you pull at, if this one thing is wrong then what else might have had a short cut taken? What else did they miss?

What  happens when you have a properly designed space is that it elicits the feelings of the room’s intent. A living room feels like a place to relax. A kitchen feels like a place to cook. There are no annoyances that get in the way or impede these activities. There is flow.