Bringing together a couple of the ideas from this thread and building on them:
What I always want to know before a gig is who are the support acts and what are the set times. If I don't know the support acts, I can then listen to them on Spotify/Soundcloud/etc and decide how much effort to put into pitching up in time to see them.
Finding out who the support acts are and what the set times are often involves trawling around FB and Twitter to see if the venue or any of the acts have posted them. And still I'm setting off sometimes knowing I'll only get them when I ask on the door outside the gig. God knows why it has to be such hard work.
If its a venue I'm not familiar with and I'm meeting friends who are similarly unfamiliar with the area, decent pubs and eateries is more info that I have to search for. Also useful to know whether the venue has decent beer/cider or is tied (02 Tuborg/Somersby - no thank you). So maybe a Dice venue guide would have mileage too.