He’s, again, a very patient demon once you get a hold of him. Everyone’s experience with the demonic spirits are all different, and that also is with how you work with them. It seems like there is no ‘right or wrong’ way to work with them, but whatever works best for YOU.
I like altars because its a constant, visual reminder that the spirit is one you are working with. For offerings of copper or roses, you can simply place copper (you can do pennies, I don’t do copper at all) or a vase of roses on his sigil. You can simply draw his sigil on a piece of paper, chant his enn while focusing on it, and tell Sallos you are offering these objects to him for whatever you want,then place the objects on the sigil. I believe the energy transference happens after all that and the energy of the physical object is transferred to Sallos in the spiritual realm. Then after 24 hours or so, I’ll remove the object. Flowers I keep constantly and I’ll refresh them when they wither.
I offer things to demons even before I ask them things because I like building relationships with the spirits, but that is how I operate.
If you are offering something to him in return for him doing something for you, let him do his thing FIRST, then give the offering. Think of it like a transaction. But I would also write down your request, sign it with your name, his sigil, and then offer it up to the spiritual realm via burning the paper, burying the paper, dissolving it in water, or letting the wind take it up. I work with the element of fire the most, so I burn everything.
Another really good demon to work with reconciling friendships is Duke Gusion. I haven’t worked with him but it seems like his original purpose is," He can answer questions and tell you why you ask them. He conciliates and reconciles friendships and gives honor and dignity to those who seek it."
He might be another one to look at for helping in your friendships.
Remember, demons enjoy working with us, as any friend or business partner would.