Some of my thoughts when I designed and built my panel for my center stick Cleanex:
1) Use a neutral color. Some colors look wonderful but can be distracting for various reasons. I chose to have mine powder coated in gray.
2) Split the panel i.e. all flight instruments on the left and engine information on the right. I have an MGL F2 Flight information instrument on the left along with my slip/skid ball and ELT monitor/switch. Also high up on the left is my Lift Reserve Indicator. Far top left is my touch screen iFly 740b. On the right I have the MGL E1 engine monitor and westach RPM gauge. Bottom right is the Flightline 760 radio.
3) Keep the area under the panel clear (as much as possible). I did violate this idea as I added a Garmin 320A transponder under the left side. It's a minimal intrusion and easy to reach and fits the flight mode side very well.
4) Separate the switches by purpose and color. The first is the master (red), the next two are ignitions (black), the starter button, then the avionics (yellow), strobes (blue), and finally the landing & wig/wag light switches (white).
5) I also put protectors around the master and both ignitions switches. Two reasons for these. First is to keep items that are placed on the glare shield from sliding or falling off and hitting the switches and turning off the master or the ignitions. Secondly, they give me a way to place a small locking/safety bar in the switches to prevent anyone from flipping a switch whenever the canopy is open for viewing (such as a fly-in event).
What would I do differently? Not much as I like my panel and it has worked well for the nine years I've been flying this aircraft. I do think I would put the pilot's side headphone jacks in a different spot. I have the jacks on each end (pilot on left and passenger on the right) but the pilot jacks should have benn placed in the center or more likely both sets should have been placed in the turtle deck behind me.
Not having success with a photo upload but the panel can be seen at the beginning of this video (all except the later transponder install):
https://www.youtube.com/watch?v=1VP7UYEqQ-g