I won't make claims for my own abilities, but I do feel I'm a good observer. I also think what works in one field can be transferred to another.
Here's a few tricks i've noticed:

1) Delay of gratification. This works in many fields. If your song seems to be resolving on a note or a rhyme, in a predictable fashion, insert something that puts it off a bit. When the release comes, it will be heightened.

2) Avoid the obvious. Similar to the above. If the listener can guess what's coming next, change it.

3) Un-natural rhythm sounds lousy. Don't stretch a word to cover two beats. Find two words that sound natural.

4) Strange but true: A semi-rhyme is often better than a perfect rhyme. Unpredictability is great. On the other hand "Life is hard and I gets tard." only sounds right if it's your real dialect.

5) Rhyming dictionaries are worse than useless. A Thesaurus, however, will turn up more interesting alternatives.