What is the best way to introduce a new dog to your current dog?

[PollutedAngel]

I have a five year old Rottie mix who has been with us since he was born. I also rescue many dogs, and there have been many dogs that have come and gone over the past few years because of this. My dog has a crate that he stays in overnight and when he feels the need to relax. None of the rescues have ever gone into his crate, so he's always had his own "space". He does get along great with our 2 cats and rabbits, and has done well with some of the dogs that have been here for a short while (mostly females).

With that said, we are looking to adopt one of the rescues that I surrendered two weeks ago as he was really sweet and I thought he would make a great playmate for our dog. My biggest concern is how to handle their first meeting, and what would be the best way for these two dogs to get along without fighting, or becoming permanent enemies. I would appreciate any and all input that anyone could give me on this as the adoption will be happening this weekend and I'd like to have a little knowledge ahead of time so I can prepare. Thanks!