There are some steps you need to take before starting a replica set deployment. First of all, you should make sure that you have the latest stable version of MongoDB on each machine.
Note
If you haven't installed MongoDB yet and need help installing MongoDB, read these short instructions at http://docs.mongodb.org/manual/installation/.
Additionally, before deploying a replica set, you must make sure that there aren't any network issues between replica set members. Each machine must see the other, and you must configure the firewall not to prevent connections. In order to have an effective replica set, you should configure the machine so that every member can connect to the other.
Note
If you want a procedure to check the connection between members, visit http://docs.mongodb.org/manual/tutorial/troubleshoot-replica-sets/#replica-set-troubleshooting-check-connection.