To understand EQ and its intricacies you need hands-on experience, but to help you get started, here’s a table of general uses and the different ranges that EQ can affect. As every sound is different, though, these are necessarily very general guidelines…
Any apparent muddiness can be rolled off around 300Hz. Try a small boost around 5-7kHz to add some high end.
50-100Hz ~ Adds bottom to the sound
100-250Hz ~ Adds roundness