One of the greatest assets to any movie maker would be the soundtrack, if it is a good soundtrack, with great songs and equally great placement, it can make an already excellent film even better.
Soundtracks are featured in every movie, and higher quality movies tend to have a higher quality soundtrack. It is very important to have a good soundtrack, and should be one of your top priorities, especially during the editing process.

Step 1: Timing

Timing is key, timing is everything. In a movie, this is highlighted very well. If a song is put in at an inappropriate time, then it will fail and the scene will reflect on that and look bad. If it is placed where it belongs, and it fits to the scene, then it can make the scene great, and memorable.

Step 2: Songs

It would be a wise choice to use a song that most people enjoy, even if the song works well with a scene, doesn't necessarily mean that it should be the song used for it. If you are using music that is unpopular, people won't like the scene, and will be distracted by the music. If you are choosing a song, you should make sure it is popular, or at least very famous, so people will automatically know what the song is.
In summary:

Popular Song, well liked
Famous song, memorable
Catchy
Make the scene better (if it doesn't improve the scene, don't use it)

Step 3: Quality

If you are going to use a song, make sure you use a high quality version. Don't get any static or feedback or it could ruin the song, and therefore, the scene.
Referring back to the likability of the song, quality should be thought of in both ways, however, it is more important to make sure the song is in high quality, so it doesn't come through poorly.

Step 4: Recording Your Own Songs

One thing you can do, is record your own music. If you play either guitar or bass, you can usually get a connector so it will plug directly from the guitar or bass into the computer. There are a wide variety of softwares that you can use, and you will also want to get some sort of amplifier software, to emulate the sounds of different amps for the instruments. You could record drums and percussion yourself, but in the end it may sound better just to use a drum machine, or tracks you can obtain from websites that give you those tracks.

Step 5: Recording 2

You should use general knowledge on editing tracks together, various recording softwares will have different settings and such, but will usually be very similar.Just use different tracks, and make sure that you get it all in time.

You should use a metronome set to the proper beat, and it will make everything much easier, at least for recording guitar and bass.

Step 6: My Movie

My first movie had (in my opinion) a strong soundtrack. My fellow classmates enjoyed the soundtrack, and we (my group) were praised for the songs we used.
We tried very hard to incorporate songs into our movie, and we were happy with the results. We felt that the songs could greatly improve our movie, and give us more options, so I recommend that you pay a good deal of attention to the songs and soundtracks of your movies.

Note: Sorry, but as of the moment there is no link to the movie, as soon as it is put on youtube, I will edit this and put the link on this page. It should be on here by tomorrow.

Link: http://www.youtube.com/watch?v=H98RgYSccKk&feature=c4-overview&list=UUU8Z3neFlSUGerlsGWzopcg