The first thing you need to do is get the right gear: comfortable swimwear, good fitting goggles, swim paddles well adjusted to your size, and possibly a training board (this last item you can easily find by the swimming pools). For this swimming material, ask a professional for assistance on what to get.
This program is geared towards working out your leg muscles with a training board in order to optimize your comfort, check the session's description and follow the coach Guidelines.
As with all physical activities, small warm up exercises are recommended before you start training and stretching exercices are recommended after you're done training.
Don't forget to drink in order to optimize your recovery.
Breathing is very important when swimming and depends on the pace at which you're swimming; Make sure you breath out (exhale) deeply and completely in the water, before breathing in (inhale), so as to optimize your comfort and your muscle relaxation.
Don't forget to put a fruit or a cereal bar in your bag in case you get a little hungry.
Ideally, try to workout on Tuesday or Wednesday and Saturday or Sunday.
Good luck.