Loading Braided main line onto your reels is very straightforward, especially if you keep the following advice in mind:
Maintain Uniform Tension
It’s important that you maintain uniform tension (higher than you would for loading monofilaments) for the whole process.
If you have someone willing and able to help, it’s simply the case of pushing the spool onto a suitable spindle (a pen will do) so it rotates and then your ‘assistant’ can use a cloth pressed on the sides of the spool to apply the correct resistance and create the necessary tension as you wind the line on.
If you do not have an able-assistant, then you can always allow the spool to rotate in a bucket of water and wind in through a damp cloth whilst controlling the pressure yourself.
Just like any line, overfilling spools can cause all sorts of problems! Especially with higher diameter/strong braided lines or if you forget to wet the braid before your first cast of a trip.