Soft proofing is a fun way to get a good idea of output quality before you click the Print button. It is VERY IMPORTANT to note that that the you should only use a properly calibrated and profiled monitor when attempting a soft proof. You should compare the final print to the softproofed version of the image after the print has dried completely.
You can experiment with the Relative Colorimetric rendering intent. The results depend on the paper, printer, and ink that you are using.
The Simulate Paper Color can be turned ON or OFF. This feature maps the White Point Tag in your profile. When this option is left off, the maximum white (RGB=255) in the file is mapped to the maximum white of the monitor (MonitorRGB=255). So the white you will see is the white point of your monitor, not the print. If you want to eliminate this discrepancy you can turn the Paper Color Simulation ON.
Simulate Black Ink maps the Black Point Tag inside the your profile to the monitor display in an attempt to reproduce the actual black density of your print. It is defaulted ON if you choose Simulate Paper Color.
Take care when using these display option simulators. The results can often look odd at first blush. It is true that the simulations work well in general. One good tip from Giorgio Trucco at Outbackphoto.com is to look away when applying the simulations. Give it a good 20 seconds then look at your monitor. This should be a good preview of your final output.
For a more in-depth presentation of ICC profile usage go to the Dry Creek Photo presentation here (link opens in new browser)