Check out these links to other swim workout websites.
United States Masters Swimming The USMS is one of our team sponsors and provides workouts for USMS members. Signing up is easy to do and comes with several benefits. Practices can be found here and registration can be found here.
General Practice Guidelines: Building endurance - keep track of yardage: Pick a target distance for the end of 6 months, Start ~600 yards below your target goal then week by week add 50 yards to your workout. Keep track of your weekly yardage and once you hit your target, take a rest week with low yardage and start ramping up to your new distance goal.
But coach... isn't that only 3 month's?
Build up your speed - keep track of cycle times: Once you reach your target yardage, figure out your 100 freestyle base cycle. Swim for 10 min straight and count the number of laps. Divide time / #lap x 4 to get your time per 100 yd. By the end of the cycle, try to drop your cycle time by 5-10 seconds.
Once you take 5-10 seconds off this time for 3-5x100 yd spend a few weeks working on sprints. Test your self with short sets of 50's and 100's with plenty of rest in between. Time yourself and log the times. See if you can improve at the end of each cycle.