I concur with Toby. 1/4 of the time upper body (use those things that you secure with your thighs) , 1/4 of the time lower body (kickboard), 1/4 combined, and 1/4 of the time treading water to help with the cardio and acts as a cool down.

I agree with Toby also;

work on your shoulder rotation, kick(with a kick board) and the breathing. I know bi-lateral breathing is not an easy part to achieve but work on it. Always remember not too look up as it will lift the head and will sink the legs, so keep your head down so your legs and lower torso stays afloat. Good luck!

Hydrodynamics are the physics that govern water. By spending time in the water, it helps to develop the natural flow, or understanding of hydrodynamics. Swimming a mile might actually help with your 25m / 50m / 500m times. There is really no substitute for swimming, but the various tools that can be used in the pool can help to improve specific skills. For instance the kick board and pull buoy. Fins and webbed neoprene gloves can also be used, either alone or in combination; kickboard and fin, or pull buoy and webbed gloves. By increasing the surface area of propulsion the generated force increases, which helps to strengthen the utilized muscles. The X-Vest is another training tool for advanced swimmers. It is basically a weighted vest, but it is also waterproof. Makes treading water more difficult, let alone moving through the water. Many swimmers also use bricks for various drills, and last semester when I took a lifeguarding class we grabbed a 5 gallon jug of water, filled it and treaded with it above our head as the whole thing dumped out. It was very challenging, and next summer I will be using this technique to cool off in the heat of the day. One last tool that I recommend for swim training is the expand-a-lung ( http://expand-a-lung.com/ ). This small, simple device is nothing more than a mouthpiece and a valve. It is used to increase the pressure required to inhale and exhale. In my opinion the expand-a-lung is better than other products like it because it can be adjusted by turning the valve. Helps to focus on contracting the diaphragm. Great to for breathing training. Other smart practice is Qi Gong. wu sa.

As mentioned before, body roll (parallel torso rotation) can drastically improve swimming by increasing each stroke length, especially for freestyle / frontcrawl. Here are some specific tips for each stroke and land exercises for them as well.

Freestyle - bend your elbows as your arm moves forward, and then drive your hand into the water. Land exercises; back extension with alternating arms extended holding light weight, torso twists, flutter kicks, and other ground abdominal work. Core strength is key.

Breastroke - pull, breathe, kick, glide. Practice the kick-glide especially, feet flexed to toes pointed as you kick. Land exercises; lat pulldown / pull ups, plie squats, shoulder circles and tricep extensions.

Backcrawl - hands enter with the pinkies, pull the water past your ear, scoop the water and push it to your hip. Land exercises; kettlebell swings, shoulder circles, tricep extensions and other ground abdominal work.

Sidestroke - keep your bottom ear in the water, this will help to bring your body more parallel. Leading hand guides, following hand pushes, and the legs drive (top leg forward, bottom leg backwards, and then together). Land exercises; front kicks, back kicks and tricep extensions.

I'm still working on my butterfly, and will keep you updated for technique tips. One more thing, don't be afraid to jump out of the pool and do some pushups or bodysquats. Overall fitness will improve swimming. Stay tuned for my up and coming book about maximizing impact while performing cannonball. just kidding. happy new year!