Sorry for the long reply but I've learned a lot the past couple of months mixing recordings for streaming videos. I'm by no means a professional audio technician, I just enjoy it, so others may have better solutions. These are just things I discovered that work for me and have given us decent results.
Duplicating and panning tracks will help fullness, panning L/R at different percentages helps instruments and vocals to stand out since they have their own place to sit in the soundstage. A lot of issues I ran into early on came from having too many vocals and instruments occupying the Center which led to them competing for space. I ended up having the best success panning almost everything to some degree. Lead vocal, snare and kick drum are pretty much the only things that remain dead center. I duplicate all of the instruments except for drums. Speaking of drums, I found that scooping out a large range of mids (big 'smile') took care of a lot of the 'pulsing' or vocal 'dropouts'. It carved out room in the frequency range for the vocals and instruments so they weren't competing for certain frequencies. On the background vocals, I have a higher low cut/high pass and more upper mids to help them cut through the mix with lower volume.
On a scale of 0-50 Left and Right, I'll pan the bass @10 L/R, which sounds more center but leaves a space for the kick, 2 toms - Rack @15 Left and Floor @15 Right, and overheads, using 2 mics, left and right @20. Acoustic is @25, rhythm electric @35 and lead hard panned L/R, adding a Center track for solos. Background vocals will be single channels panned opposite each other @10-25 but not exactly the same value as another instrument.
As far as EQ, I've discovered the easiest way to add fullness to each instrument/vocal is to use a parametric eq and have at least 4 points in the frequency range to work with. I use 5 and place them @ 60Hz, 200Hz, 800Hz, 3kHz and 8kHz. Leaving the 'curve' flat, take each point individually and, with a fairly narrow Q, use the maximum gain and sweep through the range to find which frequencies improve the tone and which are detrimental. Too narrow of a Q made it difficult to hear exactly what it was doing to the track. It's been interesting how on their own some of the tracks don't end up sounding great but in the mix sound really good.
One last thing that made all the difference to the recording was adding another Parametric EQ, quite a bit of compression as well as a Multiband Compressor, plus a moderate level of reverb to the overall mix at the Master or Output. I use the Parametric EQ and Multiband Compressor to further define the mid range and as a de-esser.