Go through your results for flights to Guernsey in United Kingdom with Netflights.
If you don’t have set dates for when you want to fly to Guernsey, try searching by month – that way, you can compare airfares throughout the year. You'll probably see that prices will be higher during April, when Guernsey is very popular, while June regularly has the cheapest prices.
So, if the flights to Guernsey don't work for you, you could always try searching for flights to other airports in United Kingdom.
For even more options, check what other airports you could fly to Guernsey from. You might be able to make a saving by going from a different airport or city.