It really depends on the fruit. For berries, grapes and other fruits that release their juices fairly easily, I'll just freeze them, then give them a quick "hand crush" with a sanitized potato masher before adding them to the must. For fruits with more structure (such as apples, cherries, etc.) I like to either get them processed thru a juicer, or I'll shred them in a food processor (leaving them as basically small bits, rather than completely pulverizing them).
That's my way - but there are lots of different ways to process fruit before you use it, and most of them work fine! The key is to break them up enough so either the yeast (if added in primary) or the alcohol (if in secondary) can extract all the character that you're after. In fruits added to secondary, take care to add as little oxygen as possible -- I don't generally food process anything that's going in secondary since I don't want to introduce the potential to oxidize my mead.