Set the carriage height to high (the white lever on the left side of the print carriage). Use all your pinch wheels that will fit. Use the roll holders that came with the printer, don't set the banner directly on the bars in back. I generally recommend using about 35c for the print heater (this printer does not have a pre heater, but when there is one, I generally set it the same as the print heater). Use the edge guides to keep the print head from collecting scrim fibers at the edge and prevent the banner edge from curling up.
I have also seen some banner material that was wound with uneven tension at the factory (a rare occurrence) that would pucker up without any heat - even before entering the printer. If this is happening, I would recommend that you return the roll for credit as you can't overcome that. Other banner materials can be super sensitive to heat, especially if not acclimated to room temp overnight. If the roll is cold, the greater temperature difference will cause greater expansion when heated on the platen and will cause head strikes.
Finally if using a take up (rare on an SP-540) make sure that it isn't pulling the banner material to one side or the other. It should wind on with very little side to side movement.
Good Luck,
Joe