the main thing to be carefull of when using flamers is that you could accidently leave yourself out of assault range by killing everything within 6"!
a good idea if you're going to make use of flamers is to either;
a) put the flamer in a transport... a rhino for example has that handy top hatch which wil allow you to pop up and pull off a 'drive by flaming' on some poor, unsuspecting enemy!
b) stick the flamer into a drop pod/deep strike with it... be cavalier! don't hesitate to try and go big and land right near the enemy! more often than not, it pays off and you can take a huge chunck from an enemy squad with the flamer before the rest of your men open up with their rapid firing guns!
cheers!