I saw a thread on civfanatics where there's a likely theory that the diplomatic relationship modifiers are not a static amount but rather a per-turn change. That means to be friendly to another AI civ you have to be a lot active in managing your relationship instead of waiting for them to denounce you.
Right now the ways to improve the modifiers I think include, fitting their primary and secondary agendas, sending delegation, establishing embassies, open borders, sharing governments, sharing religion, keeping promises, active trade(?), and liberating their cities.
Also does anyone know the difference between just ignoring requests and declining them? Ignoring seems just to avoid the penalty altogether? Ignoring seems to be the right choice especially for requests to move your military from their borders since the triggers are broken right now.