I want to start modeling an image of a Rex, the big one: T-Rex (the Jurassic Park looking one) in Blender. What are some good methods of going about that?
You can start by learning subdivision modelling, here is a good resource:
Your question is way too broad! First off, how much experience do you have with organic modeling in Blender or any other 3D suite? If you want a T-rex that looks like the ones in the movies, you’ll need to know about reference images, subsurf modeling, proportional editing tools, bump/spec/ref maps, UV texturing, perhaps rigging and skinning. If you’re new to Blender, start with modeling simpler objects and build up your skills.
Here’s a way to start, from TorQ. Make a generic reptile head, then with a few minor tweaks you’ve got a T-Rex.
Basically, begin. Post your work in “Works in Progress” and get critiques and helpful advice. If you keep at it, sooner or later you’ll have a fine T-Rex, maybe even a rigged and animated T-Rex.