Plans for an event, any tips?

[nic-e]

Alright chaps, im looking at hosting an event in Leicester at some point in the early spring.I've had some interest from a couple of companies who would be interested in running a stall and game demos, but i also want to maybe get a couple of stalls for comic books ect.
I'm still in words with a couple of venues in the city centre who are interested in hosting the event, but i want to know from those of you who have hosted events, what kind of hiccups or issues should i prep for? is there anything completely essential that i should be worrying about? and what sort of things would you like to see offered at a small event? (the venues are both cafe/bars, trendy indie places in the city center that serve good food and have dedicated event areas.so general food/drink/toilet needs are all accounted for)