Congratulations on your first lucid dream! I think what you said about visualising pleasant scenery etc. before you go to sleep is a really good idea. I also often have frightening or disturbing dreams (sometimes I end up snapping awake shouting "No!" while I think something grim is still happening), and I find imagining calming scenes and places of relaxation generally helps to make my dreams calmer, assuming I can get to sleep within a certain time-frame after beginning the visualisation, and assuming I can maintain the visualisation effectively. Otherwise, I try to imagine that there is a person whom I trust in the room with me (not necessarily someone I know, but just an abstract trustworthy figure) to act as a sort of "Dream Warden" to help ward off bad dreams. As for your dream goals, I also have a dream goal to speak with my late Grandfather, who I unfortunately never knew, but have heard enough stories about him and seen enough photographs of him to perhaps generate a somewhat accurate representation of what he was like.

I haven't actually had a full lucid dream yet, but my first lucid experience was in August of last year; I came to an impassable bridge in a dream (the midsection had crumbled away) and thought: "I'm in a dream. I can just jump over." and so I did, however, I was not really aware of the moment of lucidity, and the dream seemed to use it more as a practical tool against the dream environment, rather than letting me use the lucidity myself, if that makes sense.

Keep it up!