When you are thinking of images as you falling asleep, that serves more for dream incubation. You may/may not dream about what you thinking of. And you are right, it's best to think of something you are very familiar with. Like your childood room, mom's kitchen, classroom...

Imagining something kickstarts the dreaming process. For this, best thing to imagine and replay in your head is a previous dream that you like, or even events from your day. As you get closer to falling asleep, these scenarios may take on life of their own and develop into HH or even dreams. Or some completely different scenario will start to play out.

Once you are in a LD, you can change the dreamscape or summon a person you would like to have in your dream, if you wish.

But for keeping you aware, best thing to use are mantras.