A 1-2 lb loss a week is safe and do-able, but losing 2 lb/week can be hard to do, depending on your body. So, you could set a goal to lose at least 1 lb a week, or at least 4-5 lbs a month. Whichever you think would help better, setting daily, weekly or monthly goals. Or, you could set a minimum goal (10 lb loss by b-day) and an ultimate goal (20 lb loss by b-day). I agree that setting high goals and then not reaching them is a downer, so you'll have to break them down into manageable bits. Good luck! I'd look in the different support forums and pick a couple of challenge/goal threads to join.
Another thing that helps in achieving weight goals is turning your "plan of attack" (how you'll achieve your goal) into goals themselves, such as tracking exercise, diet and water consumption. If you set a goal to work out 3x/week, then next week, even if the scale isn't friendly, you'll still feel accomplished having met your exercise (clean eating, etc) goals.