Introducing two male cats?

[Firefoxx]

I have had my one male cat for almost 2 years, and I just adopted a new male cat from the humane society a week ago. He had an upper respiratory infection, so I had to keep them separate for a while, it'd been 9 days.. and I wasn't planning on introducing them for a few more days, and I was going to do it slowly, but one the old cat snuck in behind me into the room that the new cat is in and they fought. If I didnt pull them apart (I got bitten and scratched very badly) they would have killed each other.

The new cat was very startled, and my mother came over to visit and make sure I was okay, and went to meet the new cat and he attacked her. He is calmed down now and he is fine when my boyfriend and I go in the room to visit and feed and love him, but I'm scared he's going to be like that around new people now. I don't have the heart to just give him back to the humane society, but I'm scared him and my new cat will never get along..

But, my main point is... What is the best way to slowly introduce the old cat and the new cat together? Tips?

All feedback is appreciated. Thanks!