Start out at a very easy gearing, over 20 minutes gradually increase the resistance to a medium level. Then gradually work back to the easy gear you started with over the last 10 minutes. Purpose is to loosen your legs after a long run or ride from day before or even a recent race. If it's nice out, feel free to spin outside, but stay in the small chain ring.
WU: 300 swim/100 drill for warm up
MS: 300 swim w/ pull buoy - then 100 drill - repeat as many times as you can in 45 minutes. Swim effort on the 300s is steady - not hard, not easy. NO STOPPING.