Cabling plant is usually the first thing I tackle.
Here are some of my tips/tricks.
Number and Label every rack. (Also have a designation for front and back.)
Know the U spaces in your racks. U1==bottom -- make sure it's easy to identify that.
(you may need to tell someone someday to reboot a server which may not be labeled.)
I am a firm believer in structured rack cabling and some central patch panels.
I like to find at least two racks near the center of your area that you can bring all cabling back to..
If you have a top of rack switch, you just need enough cabling for uplinks from each rack to the center location. (maybe 4xCat5E). I always throw in some extras for growth or odd things.(serial console, management lans)
ASIDE: There are no standards to my knowledge that can use Cat6. I suggest avoiding the extra costs.
Label the top of rack uplink panel with where it's located on the other end. (Rack 20 Top goes to Rack 10, U10-12) Label each cable. Atleast with a number on each end.
So then at your center racks you can bring together all your remote racks.
Plan that out in a spreadsheet.
Here's what I call "The Octopus".
I intersperse patch panels that I hardwire back to a core switch in these same central core racks.
This keeps the rats nest off of the switch. You PRE-WIRE from the central switches to patch panels in the same rack, but spread them out. eg. Slot 1 in the core switch could go to U30, Slot 2, to U20, Slot 3 to U10.. Then you intersperse your rack switch feed panels.
eg Rack 20 could go to U29...
This means you can get away with simple short 1' jumpers to cable all your uplinks.
It's a lot of work in the setup, but I think it's worth it in the end.
You end up having what looks like a big switchboard at the center of your space, but it'll be much more manageable if you ever need to replace a card in that central switch.
I like to establish a cable color standard. Use what you want, and make sure you can source what you need. Blue=Ethernet, White=Serial, Yellow=Uplinks, etc. Make a "key" and post it to the door and above where you store the cables so everyone knows.
Get plenty of extra cables.
Get some tubs to hold supplies.
Get a label maker, some headphones or speakers, some camp chairs, a step ladder, some trashbags, a drill with good bits for your racks/servers, a small file cabinet to stash manuals, shipping details, etc. Get a 'crash cart' or a LCD monitor mounted to a pole that you can wheel around and hook up for direct machine access.
Have a lot of fun.