Step 1: Use landscape mode
Whenever possible, type in landscape mode, which offers a larger keyboard and more space between keys. Landscape is available in all major applications if you have an iPhone 3G S or have upgraded to the newest operating system.
Step 2: Type with both thumbs
Using your index finger to type is for beginners. Increase your efficiency by using both thumbs to tap the letters on your virtual keyboard. With some practice, thumb-typing will become automatic.
Step 3: Look at what you're typing
Instead of looking at the letters as you type, look at what you're typing -- it will increase your speed and accuracy. Once your thumbs know where the keys are, it won't take long to adjust.
Tip: If you touch a wrong key, slide your finger to the correct key. The letter isn't entered until you release your finger.
Step 4: Use shortcuts
Learn basic shortcuts. When starting a new sentence, simply double-tap the space bar to add a period and a space and switch your next letter to upper case. To turn caps lock on, enable Caps Lock in keyboard settings and double-tap the shift button; tap it again to turn it off.
Step 5: Learn the ABC-to-123 trick
Switching between the alphabetical and numerical keyboards takes time. Instead, press and hold down the Number key, and drag your finger to the number or punctuation mark you want to insert. When you let go, your key will be entered and you'll automatically go back to the letter keyboard.