First things first: Power. No one likes to show up to a gig and then have to spend 5 minutes hunting for a power drop and a place to plug it in. As you set up the stage, think through which musicians will need power (most do) and the most efficient way to deliver it. Typically you want to stick to an upstage power run and a downstage power run. For some groups you may not need a downstage drop but an upstage is a given. Make sure that all who need power, have it. Sound checks will go faster.
Next up is monitor cables. All of you who have gone to in ears get to skip this step, but I'm sure the case still arises where you have to throw out a wedge or two. The key is to keep cables out of the performance area, meaning the area between the drum riser and the front line of monitors. No one wants to be tripping on cables during a set. Start the cable run from the amps and end with the slack at the monitor. This allows the wedges to be moved if needed. Tuck the excess under the wedge or off stage if possible. Do not leave coils of cable laying next to wedges, its just not cool and looks bad.
When running mic lines and other signal cable, similar guidelines apply. Keep cables out of the performance area if at all possible and start your run at the snake or mic input box, not at that mic, amp, or keyboard. This ensures that the excess will be near the sound source if any rearranging or moving needs to occur. The excess cable must be NEATLY COILED IN A SMALL ROLL (this is important to a clean stage set up) at the sound source. Not piled or thrown or wadded! Also, please take the time to work out kinks, knots, or coils that may have snuck into cable, don't just lay it out in a mess. It's just not professional.
A few final tips:
-Wrap mic cable around mic stands to keep it looking neat.
-Keep all Velcro ties at the MALE end of the cable. No one wants to look at a little black strip of Velcro by the lead singer's face all night.
-Clean, straight cable runs are key. Run as many cables as you can together. It looks cleaner than having a dozen cables running all over the place.
-Keep power cables away from signal cables. Do not run them parallel to each other. If they have to cross, cross them at a 90 degree angle. This minimizes the potential for electrical interference in the sound signal from power cables.
-Hide DI boxes behind amps and risers and make sure that cable connections are not out in the open where they can be kicked, stepped on, or broken.
If you approach stage set ups with neatness in mind, you'll end up with a better end product and it will make tear down much easier. Trouble shooting and sound check are also much simpler if all cables are neatly arranged and organized. You'll feel great about your work, and all the other techs and musicians will be happier. Its just a win all around.