Bring all the recorded tracks down to the lowest possible level on your mixer, control surface or DAW.
Begin by slowly bringing the main rhythmic instrument up in volume. In most cases, this is going to be a drum set, though it may vary by the style of music. Process the recorded drums with any effects you want to use, such as reverb, delay, echo, compression or limiting. Equalize the drums so they're good enough for the final mix.
Raise the volume on the bass track (or tracks, if you used multiple microphones or blended a direct signal with a miked amp). Process the bass track as needed, and make sure that the balance between drums and bass is what you want. The drums and bass provide a rhythmic foundation for the song, and a good drum and bass mix is essential.
Bring the volume up on the main melodic instrument. In many cases, this is the instrument the song was initially written on, and is quite possibly an acoustic or electric rhythm guitar, or a piano. Process the instrument as needed and make sure the balance between all instruments present is as you intended.
Repeat the process with any other rhythmic melodic instruments. In dense mixes, there are often multiple instruments--piano and acoustic guitar, for example--that are playing very similar parts.
Slowly bring the lead melodic instruments up in volume. Lead electric guitars, horn solos or violins are often lead melodic instruments. Process them as needed. Make sure the overall mix is well balanced, and make any changes to the overall mix needed at this point.
Raise the vocal tracks until they are an appropriate volume. In most cases, the vocals will be louder than the instruments so that the words are clear and easy to understand, but this is not always the case, and depends greatly upon personal preference. Process the vocal track or tracks as needed.
Consider where all your instruments are in the stereo field. Though panning instruments is a stylistic choice, drums and bass are often close to center, while the main rhythmic and melodic instruments venture out further to the left and right sides of the stereo field. Lead melodic instruments generally move even further to one or both sides, while vocals take the center position. There are no hard and fast rules to panning--experiment!