I find that getting in the water and swimming works.
More seriously, without some other parameters it's pretty hard to suggest anything. Here are some questions you might answer:
How experienced a swimmer are you? Novice? Competent recreational? Former age group swimmer? Former collegiate swimmer?
Do you have any goals? Fitness? Competition? Short races? Long races? Open water? Triathlons?
How much time do you have to devote to swimming?
Skip Montanaro
I find that getting in the water and swimming works.
More seriously, without some other parameters it's pretty hard to suggest anything. Here are some questions you might answer:
How experienced a swimmer are you? Novice? Competent recreational? Former age group swimmer? Former collegiate swimmer?
Do you have any goals? Fitness? Competition? Short races? Long races? Open water? Triathlons?
How much time do you have to devote to swimming?
Skip Montanaro