The location for your demonstration is very important.
Usually, as the stall is not for commercial purposes, organisers of events will let you have a stall for free. However this may mean you are a second class citizen in their eyes and be largely ignored and squeezed into some appropriate spot late in the planning.
Make sure the organiser is happy to include you in their programme and on their website. Usually you will have to provide them with appropriate wording about Go, provide the BGA logo or other suitable picture or graphic, and provide contact details. At least then if people miss you or forget what you have told them they can look it up afterwards.
Now teaching Go creates a bit of noise through chatter, so it is no good being somewhere where you have to be quiet (for instance if there is a performance going on), and similarly as you need to be heard so it is no good being next to the taiko drummers or someone playing loud pop music. Usually there is an appropriate demonstration or sales area where you can be located.
You next need to be somewhere where people will see you. The entrance to the refreshment room worked very well, but under a staircase in a dark dead-end corridor did not!
If you are outside, then it may be best to be in a tent or under a veranda as it sometimes rains (or worse) in the UK. However if the weather is nice an outside spot would be grand. Watch out for wind being a hazard as stones and leaflets will blow away, or if too strong even the tent!