Break up the space you are designing in terms of "zones" and then decide how you plan to use those zones (i.e. will you be cooking while people mingle about?). Consider visual flow & decide if you want to have a clear view between the room's zones, or block it with lighting or by hanging a pot rack, for instance.
If your space is an open-concept kitchen/family room for instance, you will want to be able to dim the lights in the kitchen so they're not gleaming at you if you're using the family room. Dimmers are key in open-plan living so you can activate one space and dim the other, for instance. Think about which areas have to be better lit, such as a kitchen work space, and which should be cozier.
Some people may want a large, open Italian villa type of space; others might want a degree of separation between zones. You can create separation through furniture placement, use of area rugs, lighting or large indoor plants and trees.
Finishes should flow between zones. If you want a bright white kitchen with concrete floors, you need to carry that theme through each of your zones, so the space does not look choppy.
Give thought to electronics before you even start the renovation. Consider the placement of TVs, computers & stereo equipment. In open-concept spaces these things can be eyesores. Also, keep cords in mind when wiring outlets - you won't want to be tripping over cables in your newly renovated space!