Do you start building your GMod server? Here are the main misconceptions to avoid when developing your DarkRP server. Follow these few rules to avoid a maximum of problems;)
ULX
Do not rename the superadmin rank. Some add-ons check if the player is in the superadmin group. If you rename it, do not be surprised that some things do not work anymore.
Delete the superadmin grade. Well, I think it's the thing to do forever.
Folders & files
Folder & file names must not contain capital letters or spaces. Depending on the operating system, the behavior will differ. For example, Windows, unlike Linux, is not case-sensitive.
Addons
If your addons have not received updates since a very long time and are located on the workshop, I advise you to keep them; it may create bugs (those still on sale on scriptfodder usually are checked and therefore functional) .
Never put server files in a client folder: some data is confidential (example: database identifiers).
Minimize the number of addons in your server's collection (unless you like performance drops for no reason).
GMod Updates
I also advise you not to update servers directly when Facepunch pushes an update.
Wait a few times; a patch can fix compatibility issues after an update.