Tips for a new swimmer?

I was a competitive swimmer and a coach for several years. You'd be best off finding lessons in your area. A lot of gyms (like YMCA) and swim clubs offer adult classes or private lessons. That way, you'll have someone teaching you proper technique and giving you good feedback. If your technique is bad, you'll struggle waaaay more than you need to. Swimming is about being as efficient as possible - with better technique, you'll expend less energy AND go faster. Plus, learning proper breath control will help you out with the asthma. There's a specific pattern of breathing for each of the strokes. Over time though, your lung capacity should increase a bit, and you won't feel as winded. I had several swimmer friends with asthma and they were fine.

If lessons aren't an option for you, then there are several websites with instructive videos, pictures, etc. on swimming technique. Learn freestyle first (as it's the easiest to do over long distances) then try the other strokes if you're up for it.

One you've mastered the technique, get in the pool several times a week and slowly build up your endurance. Try to do a little bit more each time, with fewer breaks. You can definitely get up to 750m if you put the effort in.

If you need help finding a program or just have any other questions, feel free to send me a message. Swimming's a great activity and I'm glad to help people get into it!

Try a total immersion course. I have quite a few friends that used this for tri training.