1. Initially, Don't be Critical
Keeping a critical distance is vital for the reasons I mentioned above. However if you are critical from the very start of your creative process, then you will start censoring your ideas before they have a chance to fully develop. Ask youself, how many times have you taken an uninteresting sound and made it into a melody or something that involves some cool modulation? I'm sure you can think of a few examples of this in your music making process. So allow your ideas to develop first, be playful and experiment. Seperate the creative and critical parts of the process.
2. Identify the Weaknesses in Your Track
Be honest about all the sounds in your arrangement, once the intial idea has been laid down and arranged. What sounds good and what doesn't? Is something out of context? Does something need to be replaced because sonically it sounds less polished then all of the other elements? Does the texture of any particular sound let down the arrangement? Ask yourself if other people listening to your track sould notice it. If the answer is yes, then it probably needs to be replaced.
3. Don't get Caught up
It's easy to fall prey to thinking your track is great because you made it, and look! Wow! if I keep doing stuff like this i'm going to totally make it! Listen to the vibe, it's awesome! I should totally send this to a label! While enthusiasm is a good thing and a necessary part of the songwriting process that sustains you through it, another effect is that it can often blind you to the problems in the track. Does the mid range sound washed out? Is there too much reverb? Have you used the same effects on everything, causing all the sounds to become too similar tonally? These are all things you need to ask yourself. While this might dampen your enthusiaam, think of it as construcitve criticism, something that should push you to acheive more.
4. No Matter how Attached you are to a Musical Idea, if it Doesn't fit Throw it Away
This is a big one, its hard to do this sometimes. If you've made a sound using your latest and greatest sound design technique and you really want to use it in your track, realising that it clashes with a few other elements and that it neeeds to go is a hard question to ask yourself. You need to be honest, if you deceive yourself that something sounds good in the context of your track when it doesnt in the end you're only holding yourself back. Similarly if you can't polish the sound to a similar standard that the rest of your sounds are at, even if you've built the track around this sound (maybe a snare drum for example) it needs to go. In extreme circumstances this will mean that the whole idea behind your track no longer works. If thats the case then you need to accept that, and accept it quickly. You need to find a way of rationalising this with yourself, chalk it down to experience and move on. At least you're constantly learning and impoving, and at least you know you have a high standard that you are holding yourself to.
So remember to ask yourself the right questions and to be honest about the answers next time you are producing a track. Don't get discouraged, lift your standards and acheive that extra 10% that you've been striving for.