Crimping is hard, its a better connection than soldering if done right, but its hard to do right especially with the wrong tool.
If you have lots of smaller pins the line of Engineer crimpers at least have the right die shape in them:
Micro connector crimping pliers PA-09 and Universal crimping tools PA-20 and PA-21 adaptable for JST, Molex, Tyco (AMP), HRS and other brand open-barrel terminals. Also good for D-sub connectors. Featuring very precise crimping finish owing to elaborately-designed and machined dies. Crimped...
www.engineer.jp
You can find them on Amazon for pretty cheap. If you want sticker shock you can always price the "official" tool for whatever connector you have, and find its likely $500+ for a hand tool