I use the captions in my students' FLIP videos a lot to help them become more aware of the difference between what they say and how it sounds.
For example, my student was talking about the food in his country being 'varied'.
But the captions picked up 'worried'.
The 'v' and 'w' sounds are often mixed up but there's a simple way to fix this.
For 'v' put your teeth on your lips. For 'w' - no teeth on lips.
Practise with a friend - say either 'vow' or 'wow' and see if your friend can guess which one you said.
Also:
vent went
vet wet
vest west
veil whale
vain Wayne
vein wane
vine wine
vile while
Vick wick
verse worse
vine whine