Something that I have learnt over my years of gigging is that if something can go wrong, it will. A simple way to prevent any unforeseen mishaps from happening is having enough time before you have to start playing to do some pre-gig checks.
Normally, a sound check would be a great way to iron out any wrinkles that may become apparent.
The most common things that I look out for are:
1. Faulty cables,
2. Battery strength in pedals, microphones, active instruments, etc.
3. Speaker and microphone placement.
Feedback prevention should be the ultimate priority before your gig starts.
The last thing anyone wants to hear when they go out is screaming feedback.
Kill the feedback before it kills your gig!