If you know me personally you know that my day job is with the worlds largest Anti-Virus software maker. Certainly if anyone believes that every computer needs modern security software it is me. However, though you need it and it needs to be up and running and updated most of the time, perhaps an exception is when you're on stage.
Many AV products scan every file, upon every access. For digital audio and video performance this means potentially scanning massive files in real time while your computer is also trying to render this stuff for the audience with no dropouts. Since the risk that your computer will get infected is almost nonexistent during an actual performance, disable security software while on stage and save the CPU, Memory, and Disk I/O you'll desperately need for the actual show.
Learn the power of velcro
Newer Mac laptops have a cool feature of a magnetic connection from the power adapter to the laptop. They did this so that you don't' accidentally knock the laptop to the floor if you, or someone else, trips over the power cable. I know from my own experience this has saved my machine a few times from flying off my desk. That's helpful for the power cable� but what about the USB and Firewire stuff you have connected on stage? During a performance you, or other performers, or even enthusiastic fans in the crowd may unintentionally trip over cables. Stages are often dark places. You often end up not having any time to properly route cables and tape them down before you start playing. The risk that you or someone else will be rocking out and knock your machine to the floor, possibly ending the show, is actually higher than you might think.
If you can't use proper gaffer tape (NOT DUCT TAPE) to secure these cables before the show, consider how adhesive velcro strips could help secure your controllers to whatever stands you use.
Don't cross audio and power
This is a tip I learned very early on in my career and one that I see needed at almost any show I do. Do not cross cables that carry your audio signal with cables that carry power. Modern cables are usually shielded where the risk of interference is minimal, but good cables are increasingly expensive. I see more and more laptop performers buying cheap radio shack/Hosa cables that are noisy even without interference. If you cross these cheap cables with extension chords or the power cables for your equipment you increase the chance of an audible hum in the P.A.. These hums are hard to track down during sound check.
Related to this, do not plug audio equipment on stage into the same power circuits as lighting equipment. Same issue, causes hum. Not all clubs have multiple circuits on the stage but any professional venue should keep lighting plugged into separate power outlets from audio equipment.
Do your part and just make sure the cables carrying audio single don't lay over and physically touch anything carrying power.
Label your laptop
Some shows I go to look like a commercial for Apple Inc.. There are 20 people all with silver Mac Book Pros. When you sit yours down on a table or leave it on stage after soundcheck, it becomes comical to remember which machine is yours. Chances are remembering your machine is not a problem but how easy do you think it is for accidental theft to occur whenever everyones machine looks the same in a dark venue? It would be pretty easy to see how a drunk performer could pick up your laptop thinking it was his/hers after a show and take it home.
Avoid this risk by making your equipment identifiable in some obvious way. For laptops you can put stickers on them, or buy those laptop skins. For cables you can put colored electrical tape on the ends.
Bring your own D.I. Box / Scan Converter
For musicians, bring your own D.I. Boxes. These are "direct boxes" which convert the unbalanced, high-impedance output of an instrument to balanced, low impedance input of a mixer or P.A. snake. If your'e plugging your laptop interface directly into a mixer's 1/4 inch inputs this doesn't apply to you. But the most common senario you'll find in clubs is that you'll have to plug your interface into a snake on stage that runs across the room to the main house mixer. These snakes usually only have low impedance XLR (the microphone looking thing) inputs. This is where a D.I. box is required.
The problem is, most clubs and sound techs are still not used to having all electronic performers where 2 might be needed for each person (normally one for left channel cable, one for right). They might only have 1 or two for the entire system since most bands they have are mostly using acoustic instruments where this doesn't apply. Do yourself a big favor, especially on tour and bring your own D.I. boxes.
I have played MANY shows where I've showed up and either 1) the club has only 1 or 2 or NO D.I. boxes or 2) they only have a few so each band has to unplug for the next to plug in, thereby negating many benefits of doing a soundcheck at all. Bring your own D.I. boxes!
For VJs using Windows machines, a similar tip might apply with Scan Converters. Mac's have this generally built into the adapters and ports you use. But if you're using a standard VGA port on a windows laptop to project video� even if the club says "we have a projector" you may end up having your machine far enough away from it that a VGA cable would never reach. You'll need to run Composite (via RCA connection) or S-Video. To do that from a VGA port you need something called a Scan Converter. I've NEVER seen a club that has this. Consider getting one yourself (or buy a Mac. :-D )
Disable System Sounds
Similar to "disable your screensaver" for VJs, this tip is a classic. The first time I ever used a laptop on stage I sitting in with a friends band and opening for a national headliner. I was using a windows machine at the time and totally forgot to disable the default windows sounds. When I turned the machine on a massive wave of that Eno startup sound washed over the venue. Other times i've seen people get pop-up windows during a show and that classic alert sound blares out over the music.
Disable the OS system sounds before going on stage!