In talking about fantasies I have found it helpful to classify them into 3 categories:
1) never will happen, but hot for some reason
2) maybe someday, if circumstances, feelings, etc. lead us there
3) on my list of "things to try", hopefully soon!
The fantasies that fall into 1) - I look at the commonalities between them to discover what elements could be brought into our current activities and am finding that extremely helpful in discovering what might work for us today. For example, a common element is the concept of ownership - that he owns me and can command to do and/or take whatever he chooses. We have begun to bring that into our BDSM activities slowly and it has been satisfying for both of us.
The "maybe" list is our opportunity to talk about limits in a non-formalized way which seems to work better for us than sitting down with long checklists (he's just not into that!)
List 3) is just the everyday fodder for our current level of BDSM activity - he or I say "hey, let's try this", the other agrees and off we go.