There are some fabulous resources out there to help with your swimming technique.
The best resource is your coaches: talk to them, ask them questions, let them help you improve. Additionally, you might want to check out these suggestions:
The Speedo International YouTube Channel covers all 4 strokes in detail, using swimming stars to demonstrate excellent technique and practice points. It also covers some good drills.
Here’s an article by former competitive swimmer Olivier Leroy about how to hone your 5th stroke – your underwater dolphin kick: How to Develop an Awesome Underwater Dolphin Kick. Getting this to a level of excellence will improve your front crawl, backstroke and fly times no end.
Want to improve your starts? Have a look at these 5 tips: 5 Tricks for a Faster Swim Start.
Want to get faster? It’s easy – train properly: see these articles on why consistent, dedicated training is the way to improve your times: 5 Reasons You Aren’t Swimming Faster, and 6 Bad Training Habits You Should Break Now. Achievement = skills + meterage + confidence. You’ll get all those from training, if you commit to it.
The ASA has tips on how to swim faster on their website, which also contains a wealth of information about aquatics.
And you can’t really beat the techniques shown in the 2012 Olympic Men’s 100m Medley relay final…