Shit i already forgot about this thread....
Everybody pretty much already answered your question earlier in regards to knowing what frequencies to remove.
LDB added a good comment as well in regards to using an Analyzer. If your only working in Reason then there is no way to see the frequencies graphically, but its like any other platform you work in to mix. You have to just balance things out right and get your power structure going, and then after that apply effects and processing if needed.
Start with your faders, move to your pans, then proceed to asses whether u need to EQ certain things or compress. Not everything needs to be treated. If it sounds good, then it sounds good. Its easy to feel the need to process everything in a DAW environment since theres so many types of FX accessible at your fingertips.
Even though your a beginner and you might have untrained ears and poor gear everyone has to start somewhere so dont be too quick to dismiss the fact that you may have an incredible ability to hear things in the mix that others cant for that matter. The point is to try and keep at it. Your obviously not going to have amazing ears right off the bat, but everyones different is my point.
And everyone has to learn how to mix eventually if your involved in making music from point A to point B. So you might as well start now. Once you got your mix sounding decent level/pan wise without blowing up your master buss (output), then critically listen to each part in the mix and determine if it needs treatment or not.
For example, if your kick is muddy and not beefy enough, dont go reaching for the 80hz boost immediately, instead try cutting frequencies in that part that arent needed as much such as the 250 area and anything in the high end that may not be contributing to the mix. Same goes for any other sound in the mix.
If your synth part is only needed in the mix as a hi freq element then proceed to remove any low freqs by rolling the low end off until your happy, etc.....
Its always better to start by cutting rather than boosting, and just try to remember when your frequency stacking that everything is "summed" together at the master output.