The simple answer is to untangle them and be careful when adding and removing cables. When you first plug everything in, make sure the cables aren't crossed. Move from left to right or top to bottom.

If that isn't sufficient or is too much of a pain to remember there are a few additional things that you can do to keep things straight.

1. For cables that you routinely add and remove, consider using one of the methods here to keep the plugs from falling: How can I keep cables from falling off of desks when unplugged?

2. Coil and secure cables that are longer than needed.

   • You can use short lengths of velcro as removable cable ties. Double sided velcro (hook on one side, loop on the other) can be found in most fabric stores, sold in spools or by the yard.

3. Consider securing cables to the underside of your desk.

   • You can use thumbtacks or screws and lengths of velcro to secure cables to the underside of your desk like this:
     
   • Or you can make a similar arrangement using binder clips:
     

The simple answer is to untangle them and be careful when adding and removing cables. When you first plug everything in, make sure the cables aren't crossed. Move from left to right or top to bottom.

If that isn't sufficient or is too much of a pain to remember there are a few additional things that you can do to keep things straight.

1. For cables that you routinely add and remove, consider using one of the methods here to keep the plugs from falling: How can I keep cables from falling off of desks when unplugged?

2. Coil and secure cables that are longer than needed.

   • You can use short lengths of velcro as removable cable ties. Double sided velcro (hook on one side, loop on the other) can be found in most fabric stores, sold in spools or by the yard.

3. Consider securing cables to the underside of your desk.

   • You can use thumbtacks or screws and lengths of velcro to secure cables to the underside of your desk like this:
     
   • Or you can make a similar arrangement using binder clips: