Start with the basics. You can make simple (and even some more complex) props directly in Poser with the grouping tool. Even clothing. It's basic stuff but it teaches you the essentials that apply to everything else you do going forward.

With the grouping tool you can use primitives from the props library to cut various shapes, scale, rotate and move them around to assemble different things, kind of like legos. Export them together and then re-import them as a single object. You can make everything from furniture to basic clothing this way, and never have to leave Poser, at least until it comes time to map and texture them but you could use procedural materials if you really wanted to take the poser purist route.