Listen Up!
Arguably, one thing that makes great players great isn't so much their playing as it is their hearing. When listening to great players, they always seem to have a great sense of rhythm. They seem to be able to play what's 'appropriate' or 'interesting'. This comes from listening. Having great chops is one thing, knowing when to play what is another. All of this comes from listening. When playing with other players, no matter what kind of music you play, it's vitally important that you listen. You can always tell the tightest bands because the members make sure that they listen to each other. When playing with others, you should be listening to only about 40% of yourself, the rest should be everybody else. Of course the number is arbitrary, but you get the idea.
Easy Listening
There are many ways to listen. All of them are important to musicians. The first is the way you first started to listen and that's simply for enjoyment. There isn't much right brain activity, it's mostly about feeling the rhythm and melody. Beyond feeling the music, there may be some right brain activity involved in sorting out the various parts of the song and listening to the lyrics. But, you're mostly just enjoying the music without too much brain activity. This is important because this is how music is consumed a lot of the time. It's also useful when writing or listening back to your own creations. Sometimes when we write and record we get lost in the details too much and forget to just listen. This is what happens when you're right in the middle of recording. You listen back to the track but you're no longer completely separated. You're hearing the part you just recorded, your ears may be fatigued, or you may be listening to the mix. Whenever you do a lot of work on a specific track, I always suggest time to leave it. Once you've left it for a while, you come back with fresh ears. With fresh ears, you begin once again to listen like this. You hear the song, the rhythm and feel all in one instead of the separate parts. This is like the critical listening, without the actual 'technical' part.
Critical Listening Part I
This is sort of listening you do when working on tracks and recording yourself. This involves taking your performance apart and making sure it all works. This is critical in a musician's development. You must be able to sit down and critically assess your own performance. This involves pitch, timing, feel and dynamics. If you can hear the problems in your own performance, you're more likely able to fix them. It also works when writing and improvising. It means listening to your track and being able to assess if you've created the right message; to assess if it's 'working' or not. This means the lyric, the chords/harmony, phrasing, rhythm, etc. It's listening creatively to see if you're getting your message across. This is also critical in developing your own voice and style. It means listening to your dialogue and tweaking it until you're saying what you want to say.
Critical Listening Part II
This is another level of listening. This is the listening that goes on when actually playing and performing. It's the sort of listening I encourage all of my students to do. I start with playing to a metronome. Playing with a metronome isn't just about playing rhythms, it's about listening. I usually start with just practicing rhythms in 8th notes. I don't make the metronome very loud at all. This way the student has to really listen to make sure they're in time. Too often we get lost in listening to ourselves and lose track with the rest of the band. Playing with a metronome forces you to use a huge portion of your focus away from yourself. This has two outcomes. First of all, you get into the habit of not just listening to yourself but trying to 'meld in' with a group. You have to play with the metronome, not against it. So often you hear performers who seem to be in their own little world. They're in time (sort of) but they seem removed from the band and the song. This is because they're only listening to themselves and not the rest of the band, It's important that your listen to everybody else and become part of that sound, instead of simply sitting on top. Secondly, you get really sympathetic with other sounds besides your own instrument. It means you can hear any sound that you choose to focus on. It helps you isolate the kick or hi-hat when the rest of the band is playing at full boar. It makes you aware of all of the sounds going on a one time. It's great when playing with a band, you can pretty much hear what everybody else is doing (even to the point of picking out bad notes from other band members). It's almost like listening in 3D.
Combining the Difference
As you can see, there are many ways of listening. There are others but they are mostly variations of the ones listed above. Each one is valuable in it's own way. You should be able to go between each of these at will. When practicing, you want to have your 'critical listening II' going on. Making sure you're listening to everything that's going on. Making sure your rhythm and phrasing is in time. After practice, turn on your 'critical listening I' and see how your performance went. Where you in the pocket or playing ahead? Are there some interesting ideas there, or are just rambling on? After finishing up some initial takes and/or tracks, you may want to kick back and do some basic listening, seeing if it all works together. Is the message and vibe getting across, or did you make it too complicated? Make it too jazzy and not bluesy enough (or whatever you set out to do in the first place)?
Working On Your Ears
Whenever you sit down to practice, some ear training exercises should be part of your regular practice session. That means listening to and evaluating rhythms, pitches, scales, chords etc. Once you get your ear in motion and work at it everyday, a whole new world will open up for you.