Ok, here we go....
For a song to sound like it was professionally recorded, it has to be professionally recorded, mixed, and mastered.....
With that said, you could, at this point use a tad bit of compression/limiting and eq to tweak it and help bring out instruments that may have been mixed weak....fades can be tweaked....any additional noise control can be added......
basically you have to sit and listen to the mix and see what it needs, what its lacking....the advantage you have over the pros is that you can go back and remix if needed......