An app? seriously? OMG, is there an app for everything nowadays?
I think the best way to get better at something is to practice, practice, and more practice.
I have to agree with you, when in a studio I struggle to think up different poses etc.
What I have started doing is look at a few photos from togs whose work you like, and choose a couple of poses which you particularly like. Then go into the studio and try and get as close to these poses as you can. Work on the lighting, pose, etc. etc., and when you have something which you are happy with, move on to the next pose. Just work on a couple at a time, and concentrate on it until you get what you want.
I would never condone actually copying some-ones work, but it can help to use ot for inspiration.
Also, a lot of models will "know" how to pose if you tell them the sort of thing you are looking for, so it might be worth going on a couple of model shoots for inspiration, as models are a bit more patient than most "normal" people.