Here's the deal. EQ is probably the most powerful tool for correcting audio. Every commercial studio or live recording has extensive EQ applied to it. Almost all of my recordings benefit from some EQ.
The problem isn't the application of EQ itself, but figuring out what to EQ and how much to apply without making things worse. Commercial recordings are EQ'd in special highly tuned listening environments that are specially designed for the task, by people who have spent a lot of time figuring out exactly how the sound they hear in that special environment translates to the world outside where people play back the recordings on all different types of equipment.
It contrast is is very difficult for us to make the right corrections without that special environment and without a lot of trial and error practice. The corrections we end up gravitating to are those that correct inconsistencies of our particular, unique listening environments. Likewise, other corrections that should be made may be masked by deficiencies in that playback/listening environment. On top of that, even with a highly tuned and controlled environment, it takes a lot of skill to do correctly. It's very easy even for skilled professionals to fall into the trap of more is better, to end up correcting for listening fatigue or for their own listening quirks or hearing response. Skilled engineers know this and make a big effort to work in short segments, take listening breaks, and refer to other known good sounding recordings as they work.
The short and long of it is that it is very hard to know if what sounds better to you will be an improvement or make things worse for other listeners in different environments. Because of that, often the safest approach is to not do much an let other people EQ the recording themselves if they feel it needs it. If you want to try EQ'ing your recordings I'd suggest a few things:
1) Use the best, well balanced listening system you have access to and keep in mind that a lot of the EQ adjustment you will be tempted to make is due to the quirks and response of that playback system, not the recorded music itself. That goes for headphones, your home stereo, your buddy's home studio, or whatever.
2) Listen to some truly excellently produced music that you like of the same genera before starting, and refer back to that regularly while working. Use the sound of the reference recording as a comparative guide.
3) Don't keep at it for too long or try to do it when you are tired. Take lots of breaks, and re-visit it again days later.
4) It's often a good idea to use a bit less EQ than you think you need.
5) Always work at a known volume level. You will EQ things differently depending on the perceived loudness. You may want to calibrate your playback system so that you always listen with the same playback gain when you work. It may be helpful to check the sound at lower and higher levels, but work at that known level to keep things consistent.
6) When you get something you think sounds good in comparison to your reference recording. Listen to it lots of other places like in the car, on the boom box, at a friend's house, etc. and see if it sounds good there as well. Compare again with your reference recording. Ask trusted freinds who actually care about sound what they think.
If you do all that enough, after a while you’ll learn to work around the peculiarities of your environment, what translates well elsewhere and what doesn’t. That often means shooting for a target that actually sounds less than perfect on your system, because you've learned what it’s deficiencies are. The more you do it the better you’ll become at identifying specific EQ ranges, cuts and boosts. You might want to do some ear training to help with that if you’re serious about it. If so, here’s an excellent free training program I posted about here recently-
How to Listen: Critically Evaluating Recorded And Reproduced Sound 
Topic: to equalize or not? how to get started? (Read 6102 times)