A few tips: -
Don't use your crossfader at all. Set it in the centre and don't move it..
Set your cue mix to the centre and listen, with both sides of the headphones to the track playing and the track you are cueing. Adjust the volume of the cued track to match. Leave your EQs in the centre to do this. Also, try to play the "loudest" part of the cued track against the "loudest" part of the playing track. Once you're happy they are the same level (regardless of what the level meters are doing), dial out the frequencies of the cued track to suit (Bass/mid/high) before bring it in.
Never, ever have your mixer main out put pushing over 0db. This will really mess your sound up on a digital mixer generally.
Never, ever use your EQs over 0db (to boost frequencies). This will really mess your levels up.
Remember less is more, in most circumstances, so rather than pushing the levels as close to 0db as possible, remember that bringing down the level of the live track has the same effect as increasing the level of the incoming.