I know I blogged about this before - even found the photos I took - but can't find the actual post so here it is again....
When beginning a new warp I use some scrap yarn and throw 3 picks without beating. It doesn't really matter what sort of yarn although something with a little 'tooth' (not slippery) works best.
Then I gently squeeze the beater forward until all three picks are nicely lined up.
With pick number four (the shuttle is on the left hand side of the loom) I take the scrap weft around the rod and pass it to the right hand side.
With pick number 5 (the shuttle is now on the right hand side of the loom) I take the scrap weft around the rod on the right hand side and pass it back to the left hand side.
And then I pass the shuttle back to the right making a total of 6 picks to prepare the warp for weaving.