Step 3: Ignore this "advice" because it is not helpful at all. Just because one person could not learn to tune a horn, does not mean it is garbage, and I doubt you are able to get rid of your inventory and switch anyway.

More importantly, are you asking about tuning individual slides, or just general everyday tuning?
I also recommend the link listed below because it shows you which slide is for what part of the horn. As far as individual tuning slides, you can tune trigger B, Bb, A, Ab or E5, Eb, D, Db (in my opinion depending on the level of the player and what range they are playing in).
Also F#, going down for the F side of the horn.
Dont forget the hand position makes a big difference!