How to get two cats to like each other

Have your two cats avoid direct contact for a week or so. Keep the new cat isolated in their own "safe" room. Have the two cats smell each other and acknowledge each other's presence through the door - again, avoid direct contact.

Start introducing the two cats by bringing the new cat out in a crate. Allow the two cats to smell each other through the bars.

Soon, allow the cats to eat together, but in separate bowls. As the cats become more and more aware of each other, and curious, allow them to have more time together. Keep a squirt-bottle handy - you need to discipline a cat if one decides to get hostile.

It may take awhile before they cats can even stand each other - it takes lots of patience and make sure to go slowly through the process.