1- The root
Make sure to always focus on what’s most important most cases the root of the issue is the music or musician not the gear. Sometimes if a song is not sounding great it might be the song itself.
2- One Take Wonder
There have been many classic songs that were the first take but that does not mean you should only do one take. There is nothing to lose with doing more takes. This especially true with vocals which can be stitched together from multiple takes to get the best parts from each.
Bleed can make mixing a pain and can muddy the over all product. Most of the time to fix this just try pointing amps or loud sources of sound away from other microphones. This tiny change can drastically improve sound quality.
Mixing as you go will help you get a more realistic picture of what the song will sound like in the end and will help you make more informed decisions on overdubbing and the like.
5- The room and tune
Sometimes the placement of an instrument within the room can change the tone. You can use room to get the most out of the sound put up a carpet, cover concrete, and move furniture. Finally ALWAYS CHECK YOUR TUNING!! nothing is worse then getting a good take on song and having to scrap it because someone is out of tune.