If you are using a brittle glue like thickend epoxy it may help if you prime the joint first with unthickened epoxy to get some penetration, then thicken up the rest of the batch and apply immidately.

If you are using epoxy you want to go for an accurate joint. Too much gap-filling will create a stiff area in the scarf, which is ok for gradual bends along a plank length, but will adversly effect a bend accross a plywood plank, as you would get, for instance, with a tortured ply hull section.

Too much information probably.

Et