Everything is well and good above but you have overlooked the most important part. What good is an EQ if it introduce distortion to the music you're listening to (even worse if it's a piece of music you're mixing or mastering on). Instead of boosting, it's a much better practice to cut, unless you really don't have any other choice. That way you can avoid unnecessary distortion eg. If you want to boost 10dB at 20Hz, invert the boost by cutting the other frequency bands by 10dB and retain the 20Hz at 0dB. That way you can be sure that you won't be introducing any distortion to the signal path.
That's what the preamp setting is for.