I have found that multi layered goals are effective. Have a goal I know I can reach, have one that is a bit of a reach and then have one that is a stretch but that really motivates me and even scares me a little. Then, for each level, create two goals. One that is clear and measurable and one that is slightly more subjective.

While I think that having a defined time frame is important ( i.e. a point at which to do an eval of your progress), having specific parameters to meet is less critical. I mean, the point of goals is to make improvements, so if the goals you are making don't work for you, then there is no reason for making them. Everyone is motivated differently, so not all goals can be structured the same way.