The way I deal with this is to take apart one side, one flange's spokes. I place the wheel with the remaining laced side down, flat on my lap and work bench edge. I place the valve hole at my lap. Looking at the spoke to the right, counter clockwise, to the hole I note which way is radiates around the flange. (It "should" radiate counter clockwise as to keep the valve hole access as open as possible). I then look at the rim's next valve hole, second from the valve hole (the first has that initial spoke you looked at), and running parallel to that first spoke track which hole on the second (yet to have spokes at this point) flange matches up. remember a couple of things, the rim has, say, 36 holes. The hub also has 36 holes but distributed between two flanges. The two flanges have their holes off set from each other so when you look across the two flanges you see a near flange hole then a far flange hole then a near flange's hole and again the far flange's hole... So the hole at the rim that is one to the counter clockwise direction from the first spoke's will also be one, off set on the near flange, hole counter clockwise to that first spoke's hole on the far flange. I call this first spoke on the second flange the reference spoke. getting this spoke in the correct hub and rim holes sets up the rest of that flange's spokes. That far flange's first spoke and this near flange's first/reference spoke will run nearly parallel with each other. Sometimes I'll drop the reference spoke through it's hub hole and have it parallel to the hub barrel/axle and see which two holes it lines up with on the already laced far flange just to make sure of my understanding on the off setness of flange holes.

Once this reference spoke is determined then one can decide on whether the second flange's spokes will mirror the far flanges pattern WRT spoke heads in or out. But that's a different topic Andy