you need to do a lot of research before you begin. I find that during this time, the diorama changes in your mind as you read things.
You may research the anti aircraft guns and then find personal experiences in memoirs etc that change the way you imagine your scene.
I read an amazing memoirs on a guy who went through bocage country in normandy with the 28th infantry, it changed the way I thought about the fighting in that region....just the way it might change yours if you read something about the anti aircraft batteries the wermacht had.
once you've got a specific unit in a specific place that you know you can model, you can really go to town.
Maybe your tiger and your infantry are members of the panzer-lehr division, on the way to refit after heavy combat (the Ardenne for your snow setting), stopped off for fuel and rations amongst a group of AA guns ?
Just by looking here
http://en.wikipedia.org/wiki/Panzer_LehrI found a unit for your tiger and troops, and where they fought. Plus some background and tons of other useful snippets that can lead to other things.
Also, ask people to help. After I posted some sketches of what I planned to do I got a PM and straight away had access to another Armorama member's knowledge which truly shaped my diorama and also gave me tons of encouragement to carry on and not shelf the project.
Most important of all - have a whole load of fun researching and building, it's part of the hobby and personally I enjoy research the most I think. You find amazing pictures and gain an incredible amount of respect for the people you're telling stories about.