check your snare and kick, see which freqz they are hitting, then notch those same freqz out of the reese, esp pay attention to the freqz @~100hz for the kick and 150~250hz for the snare
pay careful attention to the freq range from 180hz to 500hz in the reese, this is where lots of muddiness comes in
watch out around 1000hz, esp if you have any other big synths playing, which do you want in front, the reese or the synth? take a wider notch out of whichever is not the sound you want in front
I quite like to take a wide notch out around 300hz, and then a little bit of a wide boost around 1khz or 1.5khz for some extra growl, depending on the sound i'm looking for
very very rough tips...keep at it! try not to over EQ, if it starts sounding thin, strip the EQ out and start again, pay attention to the areas that give the reese its character, and don't over EQ those areas, the more you practice, the less EQ you will need to do