I just finished my latest dedicated home lab. Which is actually my daily workspace since I work from home 99% of the time. Here are a few ideas.
AC Power: I have 20 duplex outlets evenly spaced around the room on all four walls. All wiring is 12/2 for 20 amp service. Every other outlet is connected to a 20A combo arc-fault/ground-fault breaker, and every OTHER other outlet is connected to a second 20A combo breaker. The first set of outlets are white, and the second set are black, so at a glance you know which circuit you're on. All of my normal stuff, test equipment, etc. is powered off the white circuit, and anything AC powered that I'm working on is powered from the black circuit, so if my DUT pops a breaker the test equipment stays powered and can record the event, plus they don't get cycled unnecessarily. There are enough outlets everywhere that I'm never tempted to "just plug into the nearest one", the proper circuit is always close at hand.
Lighting: Gobs of recessed cans in the ceiling, every one with 5000K color temperature floods to give me pure white light without shadows. Lighting is also on a third dedicated breaker so the lights don't go out when my DUT does something stupid.
Dedicated soldering table: Includes an LED drafting-with-magnifier light on one of those foldy-bendy arms, but its power switch has been forced permanently on. This plugs into the same power strip as all of the heated tools (irons, desoldering guns, hot air tools, etc.). It's impossible to accidentally leave the hot tools powered because you cannot turn off the drafting light without depowering them too. (My son has done this a few times and ruined a few expensive desoldering tips.)
No windows that go to the floor: This space used to have a sliding glass door, but we replaced it with a 24 inch tall sliding window to regain the six feet of wall space so more bench space could be installed. There's no such thing as too much bench space. So far we have over 20 linear feet of bench space and we're looking at adding more. It's not a dark cave, though... it has 180 degrees of windows that look out onto the lake where we live for inspiration. During the day there's so much natural light that the overhead floods aren't even necessary. Natural light is a huge advantage, both visually and emotionally, so allow for it if your location permits.
Conduit: CAT6 is popular today, but standards change. Who knows what you'll need tomorrow. So before you seal up the walls, run at least one (I ran two, to opposite walls) Sch80 conduits from your home's mechanical space to your new lab. That way you can pull coax, fiber, whatever into the lab without opening up the walls (opening walls is a PITA anyway, and just think of the dust you'll get into your equipment when you cut, patch, and sand that drywall someday. YUCK.)
Permits: Definitely take out an electrical permit, get it inspected, and get the approval sticker. If anything goes wrong, the other respondent comments about insurance are absolutely true. Don't give the insurance company an excuse to deny coverage. Plus, you don't want to miss the expressions on the face of the inspector when he sees all those outlets!
There's a few things to keep in mind that many people might not consider. I've done this a few times and have accumulated a list of features I need in a home lab. Pick and choose those that are important to you, and report back. Home labs are the ultimate status symbol, and Jim Williams was correct when he said they are almost an unfair advantage to boot.