Dwelling on something while being awake may cause your mind drift to that topic while asleep. I would recommend thinking about it just before falling asleep, and tell yourself you will dream about your friend, and then be able to recall your dream so you can record it in your dream journal.

If you don't already have a dream journal, I would strongly suggest starting one. It will increase your dream recall.

Having an LD will also give you the opportunity to control your dream so you can change it to involve your friend. I'm not the best with the actual control aspect of LDing - I can only control them to a certain extent, then I lose it. So someone else can explain that better than I could.