The rim is actually dead centre on both wheels, by that I mean that the rim centre line is exactly in the middle of the hub between the spoke flanges, so difficult to get wrong. This is true for both wheels. There are no left side or right side spokes in either wheel but on each wheel there are 18 spokes which fit to the inside of the flange and another 18 which go on the outside. Close inspection of the bend will show you which is which - the slightly longer bend goes to the outside. Lace all of the spokes into the hub, lay the rim on three blocks to raise it a couple of inches, look for any 'witness' marks on the hub where the spokes have previously been and the rim dimples will show you quite quickly the correct lay of the spokes. Fit the ones from inside the flange first and then all the others. Now turn the thing over and do the other side.
Sorry it's all words but the wheels I have just done are in the workshop and I'm afraid of the dark 🤓
I'll do my best tomorrow to take a pic of the lacing pattern but it's so foolproof even I can do it!
Ian