This is probably a stupid question, but is there any effect or something that you can use to easily see if frequencies clash with each other?
The easiest way is to use any spectrum analyser effect, i.e. the one provided with Live 9 Standard & Suite ("Spectrum")
Put the effect on the master channel, then solo each track paying special attention to peaks in the graph. Now do the same for tracks that have peaks in similar regions (or sound similarly by ear: kick & bass, bass & pads & backing synths, leads & vocals & hats/snares) and check how much the overall peak is increased. Put an EQ8 on the track that you think can have less presence (e.g. on bass, if you're analysing kick + bass; on a backing guitar/synth/pad if you're analysing them with bass for conflicting low frequencies, etc.) and apply a notch (cutting) filter there trying to find a sweet spot where tracks sound separate but still retain their character. It's also good practice to low-pass or high-pass the tracks further apart from each other, e.g. apply a hi-pass filter to leads/vocals and low-pass to kick/bass, because they can have some residual frequencies that are unimportant for their sound, but will muddy the mix.
Sorry to be so vague - it's hard to describe it really, but the idea is that each track should have its most prominent frequency (its "place") in the mix, so if two tracks occupy the same space you need to make a hole/gap - using subtractive EQ-ing - in one so that the other can sound better