I've used cold-brewed, grounds in boil, and crushed beans in secondary- sometimes just one method in each batch, other times 2 or all 3 methods in a batch. I always find cold-brewed added to secondary or at bottling the best method.
Get a French press or nylon straining bag. Take roughly 6-8 oz. water, bring to boil and allow to cool. This will drive off any O2 or chloromines. Add 3-4 oz of Coarsely ground coffee beans to the water and place in the fridge for 24 hrs. The coffee should be like "sludge"-really thick. Add to keg or bottling bucket or secondary. Usually coffee is very up front for the first month, but tends to mellow and meld.