Its damn hard to get PSU rails like that looking good, you used to be able to buy braiding for them though. Most modern (decent) PSU’s come with cable managment methods - velcro straps etc.
I used to hide a lot of my cables behind the motherboard tray and the drive bays (take off the other side of your case to do this if you want)
Zip-ties and some compressed air are two good starters.
Also, rounding your IDE and floppy cables can help. You can either purchase ones that are already rounded, or do it yourself. Essentially, you just fold the ribbon cable in a few places and hold it together with zip-ties. If you want, grabbing some split loom tubing and setting the rounded parts of the IDE cable in there with some zip-ties on the tubing to keep the cabling in place works as well.