I'll be paying a show with my band and another band next month and I was wondering if it would be bad to play more covers than originals. It's our first show and we'll be the headlining band.
"Everyone's life ends, but no one ever completes it."
Covers are great. Is this your first show, if so, I would advise it.

Covers get crowds going, and thats what young bands need.

Good luck on your first show.
1981 Gibson Les Paul Custom (Black Beauty)
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Recognizable cover songs are a great way to make the audience feel 'involved' and interested in the music. However, if you have written some really good original songs, most people will be VERY impressed to hear that as well.

I would say, do mostly covers for now. (or at least half covers) Good luck!