DO think about how you will test your code and set aside plenty of time for this. Unit tests become more complicated. You may not be able to manually test your code - at least not reliably.
DO think about thread lifetime and how threads will exit. Don't kill threads. Provide a mechanism so that they exit gracefully.
DO add some kind of debug logging to your code - so that you can see that your threads are behaving correctly both in development and in production when things break down.
DO use a good library for handling threading rather than rolling your own solution (if you can). E.g. java.util.concurrency
DON'T assume a shared resource is thread safe.
DON'T DO IT. E.g. use an application container that can take care of threading issues for you. Use messaging.
