I play with that sometimes; before sleeping think about an item very specific and tell yourself you'd like to see it in a dream and then be on the "lookout" for it

But dreams come from one's unconscious so I believe it is better to be more interested in what they have to tell me then in what I can tell them; directing too much would be, to me, like working for someone else on your days off instead of getting good rest and letting the rest revive one. Being interested in my unconscious though and accepting of it and trying to work out what I am telling myself; that has led to my dreams being more friendly and helpful to me.