You should always use a set of big speakers when mixing, like a big stereo.
Never headphones, and definetely never those silly little laptop speakers, those are toys.
What are you using? Protools or something? Always plug your laptop into a stereo for mixing and turn off all the eq on the stereo.
Then you could try playing it back through headphones or in your car or somebody else's stereo to check the results.
It's gonna sound different everywhere no matter what.
That's why studio's have these big, expensive near field monitors that are perfectly flat in frequency response
to get the optimal result no matter what the end listener plays the song through.
Also, while recording/EQ'ing, avoid boosting in a particular region too much.
This to avoid a booming low end, or harsh highs.