With Bzz Agent it is luck of the draw to be honest. I haven't had a campaign in months then sometimes I will have 4 at a time. As long as you keep your surveys up to date you'll get something eventually
Make sure you register your clubcard with them though as when you do get a campaign they pay in clubcard points (I usually get about £3-4 worth per campaign)
Good luck with your money making though
I'd recommend registering with New Vista, Populus and You Gov too as they are really good.
The 1st 2 claim to pay £1 for every 5 minutes but it is more like £1 for about every 7-8 minutes and You Gov never screen you out. You have to get £50 on all of them to be able to redeem but it adds up quite quickly