Before crimping your connector contacts to wires, the first thing to do is to prepare the wire in question. You should consider how long a wire is required for your needs. What is the wire gauge? How much voltage applied to the wire? What is the operating temperature? Etc.
Another issue to address is the shape of your hook-up wire before crimping.
After cutting the wire to your required length and stripping the insulation off as needed, you should visually inspect the shape of the wire’s strands as they may have unraveled a bit and no longer be tightly wound together as they should be.
It’s recommended that your wire’s strands not be flattened, buckled, kinked, or otherwise deformed before crimping. If the wire has any such deformities, the conductor will not crimp properly and you could have issues with the contact staying properly attached. If after stripping the wire its strands do become loose, they may be restored by a light twist to approximate the original spiral lay of the wire.
You shouldn’t over-twist the strands however. If over-twisted, the distribution of strands may be uneven and the wire cross-section will be affected, which will also negatively affect your crimp.
Please note that the proper connector and crimping tools are also important to providing a more consistent and reliable crimp.