1. Try using "Yes, but" / "No, and" format to heighten stories' conflicts.
2. Have a character think about doing something, yet not do it. Great character-building strategy.
3. The closer the resolution to your plot lines are to each other, the greater the effect.
4. Find what your character wants most and watch his emotions as he tries (and continually fails, typically) to get it.
5. It can be beneficial to set up medium arcs, larger than subplots but a little aside from the main arc (or even an independently-bound chunk of the main arc), to add periodical high-points triumphantly.
6. You learn a lot about characters by how their reactions to the same events differ.
7. For a successful resolution, build a satisfying framework in the early chapters before the conflict gets hot-'n'-heavy. Once your characters have been through the wringer--pop--resolution.
8. In most cases, characters were not born yesterday. They had lives before the story began. Use background information to your advantage and make sure you have enough so that your characters don't feel born of the plot.
9. Weapons break.