Here is some advice from SPT's professional triathlete Morgan Chaffin:
As a triathlete and masters swim coach I see people on a daily basis looking to get faster in the water. First thing is first it doesn’t come easy. Efficient swimming is 100% driven by stroke mechanics and the able to “feel” the water. It takes time to develop swimming skills and it takes A LOT of practice to engrain the muscle memory of a smooth, effortless stroke. Since I’m a triathlete and focus mainly on freestyle I wanted to share some freestyle drills that might be beneficial to you if 1) you’re looking to get started 2) you’re a triathlete or swimmer looking to refine your stroke 3) You get bored and want to mix it up! The four drills are listed below along with great YouTube demos!
1) Catch up drill: This drill teaches body roll and reach to catch as much water as possible out front. http://www.youtube.com/watch?v=Fszey7mJSb4
2) 6 beat kick-switch drill: This drill teaches good body position in the water while focusing on breathing to both your right and left side and emphases kicking. http://www.youtube.com/watch?v=HWrAYcmexqQ
3) Fist drill: In this drill you swim with your hands in a closed fist. Without your hands you will feel an exaggerated pull with your forearms. http://www.youtube.com/watch?v=4E5PhoJoR7E
4) Shark fin drill (there are several variations): I use the shark fin drill with a kick board when swimmers have a tendency to swim flat with limited body roll. Place a kickboard in between your legs (above the knees) and proceed to swim normal freestyle, but with every stroke you reach around and tap the board which will cause you to rotate your upper body and hips.
I hope you find some of these swimming tips and drills useful! If you have questions about them email me at firstname.lastname@example.org! Happy Swimming!