Everyone does them differently, paint on the kit when glued or paint off the kit then glue on the painted kit.
Generally it would depend on the kit. The Bradley you are doing has side skirts. Are you going to fix them before painting? If so the tracks will need to go on first
What I have done to the kits I have, is prepare the tracks in two halves, an upper and lower run, then paint each half separately from the hull, then fix them in place before weathering. Firstly make sure that you have enough room to remove the track if the wheels are glued down. If not, use a bit of blu-tack to hold the wheels in place whilst you prepare the tracks.
Doing one run at a time, glue the top links and lengths together as per the instructions so that the ends would be half way around the idler and Drive sprockets -make sure the edge is in a straight line by placing the links against a ruler or something with a straight edge as you glue them together.
Let the glue set a bit then place them in position and gently push the links around the idler and sprocket but don't glue them to the kit. Let this set completly and if loose on the kit then use a little blu-tack to hold it in place. Then do the same procedure for the lower section making sure that the loose end links fit in the upper row links at the proper angle but don't glue them together yet.
When completely set you should be able to lift the track off the idler and forward off the drive sprocket for painting. Finally Glue them back on the kit when the rest of the model has been painted - don't use the poly cement as it won't join through paint, use cyano instead. Glue the track onto the road wheels and return rollers for added strength.
Hope this helps