In most cases, the easiest way to avoid stress and panic, and enure everyone has a great gig, is to be prepared.
1) Bring everything you need. That means your instrument, spare strings/sticks, jack lead if you’re an acoustic artist, power packs/batteries, and extensions leads. Don’t assume that the equipment will be at the venue. Even if it is, it’ll take time to find it or find someone to borrow from, and it shows a lack of preparation.
2) Know your set. This means rehearsing, and learning your lyrics – but also coming with the order of your set planned out (ideally printed with a spare copy for the engineer if you have any notes on sound/lighting cues, and if you’re playing covers, one for the DJ so they avoid crossing repertoire). Plan a song to soundcheck with (usually the busiest, with the most BVs and best mix of instruments). Also plan an encore.
3) Understand the curfew. Don’t expect to get an encore unless you play really well, but equally make sure you finish your set a litte early, and don’t stand around for 5 minutes deciding what to play, before the stage manager pulls you anticlimactically offstage.
4) Rehearse the setup/packdown. This sounds silly, but the bands that do it are ninjas with their setups. There are tips on this blog, but learning your own setup and the quickest way to get on/offstage will earn you love and respect from bookers, promoters, stage managers, and engineers.
Alternatively – rock up late, bring broken or incomplete equipment, ask your audience which songs to play and when, take a toilet break right when you’re supposed to be onstage, run over your set time, and see how many venues are eager to return your calls…