包括两部分吧：

private function initLogger():void {
            myLogger = Log.getLogger("MyCustomClass");
        }

        private function logLifeCycleEvent(e:Event):void {
            if (Log.isInfo()) {
                myLogger.info(" STARTUP: " + e.target + ":" + e.type);
            }
        }

    private function initLogging():void {
            /* Create a target. */
            var logTarget:TraceTarget = new TraceTarget();

            /* Log only messages for the classes in the mx.rpc.* and
               mx.messaging packages. */
            logTarget.filters=["mx.rpc.*","mx.messaging.*"];

            /* Log all log levels. */
            logTarget.level = LogEventLevel.ALL;

            /* Add date,time,category,and log level to the output. */
            logTarget.includeDate = true;
            logTarget.includeTime = true;
            logTarget.includeCategory = true;
            logTarget.includeLevel = true;

            /* Begin logging. */
            Log.addTarget(logTarget);
        }

最佳实践：
  1. get Logger by class
    private static const LOG:ILogger = LogUtil.getLogger(MyClass);
  public static function getLogger(c:Class):ILogger
{
    var className:String =
        getQualifiedClassName(c).replace("::",".")
    return Log.getLogger(className);
}
  2. 将LOG声明为 静态常量
  3. format log string consistently
    LOG.error(
    "Something bad has happened: event={0},message={1}",
    event.type,
    message);
  4. 使用filter进行过滤，而不是某些特殊字符
    target.filters = [ "my.important.package.MyClass" ];
    target.level = LogEventLevel.INFO;
    ...
    LOG.info("My important message");
  5. 在logger输出前加入 if条件
    for (var i:int = 0; i<10000; i++)
{
    if (Log.isDebug())
    {
        LOG.debug("Blah blah blah: i={0}",i);
    }
}

flex端的日志

blaze-DS日志

参考资料：

   http://hi.baidu.com/%B1%E0%B3%CCabcd/blog/item/6fe0f7bec1928e0319d81fb2.html