fan assisted ovens are generally 25 degrees hotter than it says on the dial, so if the recipe says 180 degrees put your dial at 155. it is hit and miss though as each oven is different
reduce the temp by about 20 degrees and time by 10 mins or so depending on overall cooking time. They are all different so, like any oven, there can be some trial and error. I have just moved house and have inherited a conventional oven and will be going back to fan as quickly as I can. Having said that there will be other people who swear by conventional and some prefer gas to electric.