How do you add fruit to beer?

The main thing to worry about is contamination and adding fermentable sugars that could cause uncontrollable secondary fermentation in package.  From speaking to other brewers, the best time to add is 1 day before the end of fermentation, any sugars will be fermented while maintaining maximum flavour. 

As the fermentation is active the yeast will suppress any potential contamination from the fruit.  Take care to get the yeast count low in pack to limit the risk of secondary fermentation and pack the beer at the end of the week to limit any cross contamination.