Need mixing tips, articles, links

[Papersen]

We`re about to complete the recording process of our new album. We`ve done some mixing already, but still face the problem that some songs are too "plain". They lack depth and clarity sometimes.

Since we want to mix the stuff ourselves, we`ve taken some tips / advices from an engineer. He said that some instruments were sharing the same frequencies and should be EQ`ed to get better results.

Since I don`t know what frequency belongs to each instrument
(voice, bass, drum kit, clean guitar, distorted guitar) I`d like to know where I can find that info.

Thanks