I was in a similar situation to you. I am a sophomore this year on the swim team, I started this year. Last year I tried out and made the team because there were no cuts, but I was not in shape and didn’t think I was ready to swim competitively. For the entire year following that, I went to the lap pool 3-4 times a week on my own and swam around 1 mile each time. At first, I could only swim about 50 yards before taking a break. By the time it was November of last year I was able to swim over 500 yards without stopping. I think the best thing you can do to get in shape for swimming is just to swim. Weight lifting and other exercises can help too. Keeping all of this up over the last year allowed me to keep up with people on my team that have been swimming longer than me, and I’m able to place pretty high in some events like 100 freestyle. I would recommend practicing form for each stroke too. Freestyle has always been my best stroke, but you may be great at back stroke for example.