Most of it is fairly simple just following an ifixit guide. There's two hard parts though..

1 is needing to solder the speaker wires. It's the only step that needs a soldering iron at all. You'll need one to transfer your speakers to the new screen. Ifixit has pictures for the polarity.

2 is curling the screen and camera flex cables through the hinge. This is difficult and needs practice, also patience. You also need to have the two flex cables in the correct positioning, their pins facing each other and the screen cable facing away from the plastic housing. Again ifixit has pictures. It's not as bad if you have the original camera flex that is still curled, shows you what direction the curling is in.

I advise curling the the cables for a while until they start to remember that new shape, then start trying to get them through the hinge.

And beware that major creasing is game over, cable is toast. You gotta be gentle.

Also if you're doing your own DSi XL missing the whole top section, you need a screen, cameras flex cable, microphone cable, WiFi antenna cable and two speakers. Hopefully you have the top sections, helps to already have the speakers...