One of the best tools developed for designers in the past few years in Google Sketch Up. First of all, the basic version is free so you aren't investing thousands of dollars just to learn the program. You can mess around stress free for hours and hours until you get the hang of it. Secondly, unlike Autocad and other more complex rendering programs, it is very intuitive. You can start making decent looking models soon after you start. Third, there is a library of furnishings and materials that others more versed in the program have created and shared so you aren't spending a chunk of frustrated time trying to create an Eames lounge chair. You can just plop it into your model. Actually, a lot of architectural and interiors companies have their products officially modeled top encourage you to use them in your models and ultimately specify them. And lastly, I love the way the renderings look. They aren't photorealistic at all. There are other programs for that. They look like a very well drawn 3D view I would aim to create by hand.
Here are the development drawings for an office build out I am currently working on. Rendering brings the 2D space plan and elevations to life and communicates more confusing concepts to make sure the client and the builder fully understand what I would like to build. I love being able to "build" the model virtually and then move through it, peek in and out of rooms, reconfigure furniture before even one dollar is committed to acquiring materials and furnishings.
Modeling the space helps figure out the right proportions and view the design from many angles so you can be sure its going to look right. It also helps the client envision it. By the time the space is actually built out, it has lived in my mind's eye and the computer for long enough to feel familiar to me. I highly recommend you get versed in Google Sketch Up if you are about to remodel your home or need to represent your design ideas. It will make a big difference in the overall success of the project.
*Totally 100% not a sponsored post. I am simply a huge fan of this software*