What's your goal?  Do you want to get into shape?  Do you want to get into competitions again?  You need to figure out what you want out of the swimming and then go from there.  If it is just to get into shape...start with a reasonable goal such as "I will do X number of laps...then each time you go bump it up a bit.  Also, get a swimming buddy to motivate you when you don't feel like going and do the same for that person.  Good luck!