I have actually been practicing on this myself, but so far have only been able to enter people's dreams. The dreams that I do enter are people that I am closely connected with, but I never tell them that I'm actually doing it. Because my friend usually tells me her odd dreams, I hear randomly afterwards that they dreamt of me, but their perception of the dream is usually different. For example, I dream of a friend (whom I have to always introduce myself to) and in my dream, she is driving my car. But in her dream, it is her car. She does not recognize me (as I look like a stranger) but she accepts me after I remind her of who I am. The car situation makes sense, as it was her dream, and therefore her thoughts were "my" car.
Usually before doing any of this, I take time, light a candle, internalizing whom I will dream of next, and focus on my intentions. Sometimes I write the name down several times in my spellbook/journal. I then do not think of the matter again or before I go to sleep. These dreams are usually my very first dreams of the night, and I am quick to realize their importance.
While I fear the invasion of privacy towards others, it is the reason why I choose only people close to me. Unfortunately they all have very strong personalities which may be the reason why I fight against them for control in the dream.
Not sure if this helps. I'm not formally trained, but let me know if you make any progress!