[Nonfractal]

Keep 'em clean (zippo) and well shaped. Check before every race.
 Cut at 90 degrees just before the end of the guide blade. Anything other than 90 causes the braid to split apart and shed.
 Inox , even for analogue racing. 
 NSR 0.2 untinned race braid is my braid of choice for all types of racing (everyone has their own preference)
 Ensure the braid has a little vertical give at the front by creating slightly curved braid exit from the guide (not a hard 90 degrees) 
 A hard front edge can trigger straight line "W-T-F?" Deslots when it hits track imperfections at high speed.
 Be sure never to allow your eyelets or set screws (whichever you use for cable fixing) to protrude below the track facing surface of the guide.

 Splay the braids  out from the centreline of the car if you are racing on track where the rails are wider than scalextric
Use your setup plate to ensure that the braid is contacting the rail surfaces as you would expect. 
When changing a braid, change both ! (Don't be a cheapskate with your  braids)  
Alan