I don't know a whole lot on the right way to do things, but when we got our second dog these are a few things we did:

First introduce the dogs on neutral territory. Give them a chance to sniff each other out and then take them into the house together.

Give your current dog lots of attention. Let him know he is not being replaced.

Let the dogs adjust to each other on their own terms. It will take awhile...don't expect them to be bust buds overnight. If your older dog feels threatened, he may revert to old behaviors you thought you had dealt with.

I think that is a start. once you get your new puppy home, you will see what kinds of issues crop up. There are lots of people here who have great advice and will try and help!!!

Good luck and Congrats on the new addition!