wasps come where there is food for them. so...cover food and drinks if eating outside, clear windfalls if you have fruit trees. Nests can be destroyed with wasp nest spray from a diy store. It shoots a jet of insecticide at the nest from a safe distance. If you are really infested, say in your roof space, then get an exterminator out as he will have protective gear and stronger chemicals. I'm not sure that wasp traps are really helpful as 1 they attract wasps and 2 if there is still a food source, more wasps will come to take the place of the dead ones. Also you might be reincarnated as a wasp one day!