As you mentioned, EQ can be very helpful. Sometimes it might be easier to use a low pass, high pass or band pass filter instead of graphical EQ, but it also depends on a specific track.
You can also play with stereo. Often, some instruments are in the center of the stereo image. Most typically vocals, bass, kick drum. You can emphasize them by mixing the track to mono.
If an instrument is panned to the side, you can split the track to separate stereo channels and mute the other channel, or play with the pan slider.
If you split the stereo track to two mono tracks, and invert the phase of one of the channels, you will remove the mono instruments panned to the center, which are often the loudest. Sometimes it may help to slightly adjust the volume of one of the stereo tracks.
Changing the playback speed is another useful trick. Slowing down without changing the pitch may help to transcribe faster sequences. However, changing the playback speed with changing pitch shouldn't be dismissed, as it introduces fewer artifacts. Slowing down a recording by 50% will pitch it down by an octave, which is fine to transcribe high-pitched solo instruments. Less often, one my try to increase the speed, to bring the bass notes to higher, better audible range – but of course this works if the bass line is not too fast.
All the above is possible to do in audacity, or with many other audio editing software.
Playing back the recording at various volumes may help, as the ear frequency sensitivity changes with the volume. Also, it's often easier to hear small details on headphones. Just take care of your hearing and don't listen to the music loud for too long.
Last, but not least, practice. As you transcribe more songs, perhaps also helping yourself with scores, when available, you will get better.
