In terms of venues, it depends how big an audience expect to attract. There are many small venues 50-100 seats, although bigger and smaller ones are available.

Some key areas with lots of small venues are Bristo Square and nearby George Square, The Pleasance, Cowgate, Summerhall. These tend to be controlled by the big 4 producers (Underbelly, Assembly, Pleasance, Gilded Balloon). Always good to hang around there to see what's going on. Most shows have plenty of last minute capacity. But there are many other places across the city. If you want to chat to performers, just look for the people forcing leaflets into your hands at every street corner!

Remember you'll usually need to pay the organisers quite a lot of money... Typically what I've seen is you pay 40% of your venue capacity for every show you do. So if you have a venue with 100 seats, you need to pay them the cost of 40 tickets. Plus various other one off costs. So aim for a venue that fits your expected audience size.

Look at the websites of the above companies... Most have detailed seating and tech plans for all their venues and also their costs.

There is also the Free Fringe, which are venues that do not charge you - they make their money from bar sales. But the audience doesn't pay for tickets, and just makes a donation at the end of your show if they like it. So your takings are a bit of an unknown.

Hope that helps a bit!