Set up your tracks in the mixing environment of your choice. Whether a hardware mixing board or a software mixing suite, the basic terminology will be very similar.
Listen to the song all the way through without making any adjustments. Use this as an opportunity to decide what the track requires to sound good. For example, note if certain parts are too loud or not loud enough, or if the bass and vocals, if any, need increased presence. Write down some notes on your observations. These will be your basic guidelines when mixing.
Play the track back a second time. This time, set the relative volume of each track in the mix. Move the volume fader on each track up or down to increase or decrease volume. For example, unmixed drum tracks are often too loud relative to other tracks. In this case, the volume fader associated with the drum track should be pulled down. Vocal tracks, by contrast, often need to be increased in volume. Adjust the volume of each track until you are generally satisfied with the way they sound together.
Set the panning parameter for each track. A useful metaphor for understanding panning is to picture yourself as an orchestra conductor. The conductor stands at the center of a semi-circle of instruments. From her perspective, each instrumental section has its own space in the overall audio field. Panning when mixing should be thought of in the same way. As much as possible, each track should occupy its own space in the audio field. Vocals are generally center-panned, as are drums. Accompanying instruments such as piano or guitar are often panned to one side, as are backing vocals. Experiment with different panning schemes until you are satisfied with the way the tracks sound together.
Equalize each track, beginning with the dominant tracks such as the lead vocals, drums and lead guitar. EQ is handled in a similar manner to panning -- each track should occupy its own space within the overall frequency range. For example, the bass track's EQ will generally emphasize bass frequencies, while the vocal track will have equalization emphasis between 200 to 300Hz.
Add compression to any tracks with very pronounced dynamic contrasts, such as drums and vocals. Compressors serve to even out the overall volume of a track, increasing the quieter parts in volume while reducing the volume of louder parts. This helps the track "sit" better in the mix. Most compressors have built-in presets for specific contexts, such as drum or vocal compression.
Listen to the track all the way through after mixing. Make any obvious adjustments. Leave the track as it is and come back to it later. Giving yourself a few hours between mixing sessions helps to keep your ears better attuned to problems. When ready, return to the track and repeat Steps 4 through 7 and take another break. Professional engineers will sometimes spend weeks mixing a single track, depending on their personal standards and the result they want to achieve.