Expect nothing but happy friendly people. Don't expect anything and it's usually men go dressed smart. Look in th club section for clubs in your area and read the reviews.
Try to relax, your experience will depend on which Club you go to.
Look out for special newbies or Freshers Nights.
Checkout the Club reviews forum on here.
Honestly try not to be nervous, swingers are very friendly people. Nicest club experiences I’ve ever had. You’ll be fine. If you can, aim for a club they has a dance floor etc as I think it’s less scary and then you can go explore rooms if/when you feel brave enough. Good luck x