Telling your subjects/collaborators that you’re changing direction may be a little confusing to them. In most cases, they don’t know and don’t really care. Simply make up your mind on how you want your work to look, then do what it takes to get the model/subject to help create that vision.
My only suggestion - make sure you’re not following a fad when you do move forward with your work. And, if the subject isn’t getting it, don’t get mad at them, come in with a new approach - either with them or with the next model/subject. I also found it useful to work outside your regular system when trying to get a new look (so, for instance, I normally use models from the best agencies for 99.999% of my work but occasionally I will use friends, people I meet out, find people on sites like Craigslist, ModelMayhem or Facebook, or do a street casting. This is especially good when you’re trying something that makes you feel uncomfortable).