Originally Posted by Lakers4Life
I usually push the gripper until it holds the string then start applying tension. But it may be different on a DW, you almost need another hand.
On a linear gripper (like the NEOS/WISE), you can also angle the string towards your body, and the little resistance will close the gripper for you due to the bend in the string. IMO it's not ask awkward as trying to fiddle with the gripper themselves (pushing it in to close on the string). Less chance for the string to pop out while tensioning, too. This allows for one handed operation on tensioners with the tensioning switch mounted close to the grippers.
On a rotating drum gripper, I'd recommend doing a double wrap around the jaws if you have the luxury. You can also improve the clamping of the jaws by holding the jaw shut while the tensioner begins working, or doing a similar "string bending" method to encourage the jaw to shut. I will go with a double wrap if you've got the luxury of spare string.
Edit: while it doesn't really apply in this case, if you have a SPARE starting clamp, you can also put it on the out-side of the rotating grippers. The drum will shut, but what's actually important here is that there's no slippage, and the starting clamp will obviously prevent that.