A common reason recordings don't sound "pro" is often because of the arrangement. Yes, we can all often use more gear a new mic, preamp, or the latest plug-in but the fact of the matter is that very good recordings have and can be made using very inexpensive, basic equipment. I know this isn't what people might want to hear, but chances
are very good if you already have some type of recording set-up that you can make great-sounding songs if you dig a little deeper into what you're actually doing rather than digging deeper into your wallet.
I hear quite a few people who are good musicians who post MP3's around on the web for comment. I hear very few people who are actually good arrangers.
Many home recordings have a few things in common:
1. Showing off/Overplaying: The players are too busy showing you that they can play their instrument and that they're good, and forget to come up with perhaps the simple part that works for the song.
2. Holding it together: The lack of counter melodies and musical hooks. What many people tend to do is write a song, and then when they record it all the instruments just sort of comp to the root. No real tension is introduced. No additional musical ideas. I hear this a lot.
3. Insecurity: [ This is also true of live bands. ] People often do not explore their instrument enough to be secure enough to develop their own style. So, often it just ends up as the sort of boring, take-no-chances MOR stuff. [ personal and spiritual development might also be included here ]
4. The Silence: I don't think people realize that it's often what you don't play that can make a song really work. Home recordists tend to cover up the canvas completely in an effort to make something sound big and full, and miss the idea that the space in the music is a huge factor in making something truly palitable and tasty.
5. Doing too much: People who record at home often try to do too much by themselves rather than enlist help with the project. Too many people now "play everything", not really because they actually do play all the instruments well, but rather because they're too lazy or lack the skills to work within a larger group towards a common goal. Let's take the average major label CD release and we'll say that everyone who worked on it has an average of 10 years experience. You've got a band of 5 people. 2 engineers. 1 producer. 1 mixer. 1 mastering eng. That's 10 people! Multiplied by 10 years each and you get a total of 100 years total combined experience. That's 100 years [ and in many cases in the real world, it can be 200-300 years ] of sweat and experience competing with the average home recordist who may have several years experience with a few instruments and a few years recording experience.
6. Lack of experience: Plain and simple. This part's OK, and everyone has to go through it. Everyone has to start somewhere. Suck for awhile. Don't worry about it. Have fun.
7. Tones and timbres: Another very common "home" problem is that many people just simply don't know how to get the "right" sound on any given track to work with all the other sounds that just aren't quite right. A song has to be this kind of one world/thing that all works together as a single creation. This is an art and a craft unto itself and takes years and years to learn how to do well.
8. The "seams": Just like a finely-crafted coat all the seams need to be in place. Home recordings often have lots of seams showing and rough edges that don't match up well. And much of learning to make fluid music and recordings goes all the way back to the arrangement.
9. Living in the past: I notice this, especially with some of the older crowd. They just get stuck in some timewarp in a certain period or genre that has come and gone. And this is not a criticism of "classic" music, but more about the approach used when recording. Many older musicians have experience playing live, but less so with recording. It's important to realize that there can be a difference between what works for a live performance and what works in the studio. They are two different worlds, so be open to new approaches for working in the studio.
10. Listening: People who make the average home recording often haven't learned to listen. To just listen is probably the hardest part.
This list is by no means complete, but it hopefully offers something to get the wheels turning towards making better recordings.