Now that you have them all lined up in one project, listen to each one. Take notes, actual notes. Listen for the differences between each song, paying attention to how much energy is in each freq range. Pay attention to how loud backing instruments are to the lead vocal, the kick, the bass, etc. Does each song match in this regard? Does the overall feel match up?
Compare similar songs to each other. Hard rock to hard rock, soft acoustic songs to soft acoustic songs. Compare verses of one song to verses other similar songs, do the same for the choruses, the soloes. Bounce around. Note all the differences. Pick one song that clearly defines who you are and sounds like your best effort. Deem that song the golden song and plan to make adjustments to match the other songs to the golden song. I use the lead vocal as the one element to compare loudness between each song.
If you find large discrepancies from one song to another, you should go back to the mix and fix it there. If the differences are little, apply some processing to make adjustments. Here's a little tip.... If all your songs are in Reaper, instead of putting them all on one track, split them out to individual tracks, but still maintain the spacing. Song 1 is on track 1 and ends at 4:00; Song 2 is on track 2 and starts at 4:02, etc... That way you can use plugs for each song individually if necessary. Then put a compressor and/or limiter on the master bus. (Hint: That's where you will get the volume up to commercial levels.... A whole 'nother thread, right there!!!)
Once you have done all that, render the entire project to a .wav file. Then you'll have to find a way to make a DPP file. This is where I can't give any suggestions. I use Wavelab for my mastering software and it will create the DPP stuff automatically and burn an Audio CD for me. I can then send that Audio CD off to a duplicator or replicator (I can't remember which is which); Kunaki.com is my choice. Hopefully someone will chime in on what to do with the .wav file.
After you got your CD burned, take it to the living room, listen there. Take it to the car, listen there. Take it everywhere else you can play a CD and listen to it. Burn some of the songs to an MP3 and listen on your phone and earbuds. Take notes on how it sounds and what is wrong, then start the whole process over again.
Yup, you'll have to do it multiple times if your listening room isn't treated properly.
The one nice thing about sending your mixes out to a real mastering engineer is that he can "remove" the home studio feel from a song. He can't fix my boxy vocals or poor guitar playing, but he can compensate for the poor mixing room. At least to a point.
