How can I use the Flex Tool easily on LDD? On LEGO Digital Designer, I find it very hard to move the piece being flexed to the correct position. 

Are there any tips or musts that I should try to help me flex it into clips etc.?
This eurobricks thread has several LDD tricks, some of which use the flex tool.

Please be aware however that LDD can easily crash from using the flex tool or the hinge/hinge align tool. 

There are other tools to flex parts but they are not as simple to use as LDD's flex tool.