Speaking as a Dubbing mixer id suggest
1) Be clear on how suitable the speakers are you are listening on. Edit suites / avids etc generally dont have studio quality monitors attached. Why would you? But if youre making eq decisions based on your ears (and thats the most important thing) how do you really know what youre listening to compared to the end audience????
2) Never over eq unless its for dramatic effect, and once youve set it so it sounds the way you want it, dont keep going back to it and re pusing the eq. Your ears will aclimatise to the new sound, and continually re visiting it will make it way over baked in the morning.
3) do listen to your mix on a variety of different monitors. makke a dvd and listen on different tvs so you have a real world experience rather than trusting your edit setup..
In general terms, your dialogue should be crisp and clear with some warmth, but not overly sibilant. The clarity is in the 5k - HF range.