Problems crimping Cat6 Ethernet
Well, if you do normal house/building wiring, you don't crimp plugs on anything, you just punch-down into jacks (one wire at a time) and buy patch cables pre-terminated. That's what a professional job looks like, and there are good reasons for it - one of which is that getting wires into plugs is fiddly, even with experience. Another is that building wiring is solid and not meant to flex, while patch cables are stranded and survive flexing much better, so using patch cables plugged into wall jacks rather than plug-terminated building wires sticking out of the wall leads to a plant that survives longer.
The type of plug you use, if using a plug, can make a large difference - some are much easier to get the wires into, and some have cute tricks such as being able to feed the wires all the way through the plug and beyond, and then having a crimp tool that cuts off the excess, so that you can have minimal untwisted wires without having to get everything trimmed perfectly before shoving it in.
The main trick with lining up the wires for a plug is to get the twist out as far as needed (but no further), and everything lined up, and trimmed evenly if not using one of those cute trick systems with the post-trimming. This usually involves using pliers on the individual strands to remove the curl, and several insertions in the the plug to verify where a straight cut across the end should be located, and that all strands are in proper position - by which point you would have been done with punching down a jack and moved on (speed, another advantage of using jacks to terminate.) Often a certain wire will decide that it wants to hold back and not shove in even with everybody else, and you have to sort that out.
As for holding them while inserting, pretty much just pinch between thumb and finger after having got the curl out and the wires lined up correctly. Then visually inspect to be sure they are still in the right order and fully inserted.