@Flobear Number your rows, either horizontal or vertical, according to how your mind works. Make sure you know which way is 'up'.
You can sew blocks into rows/columns and then rows/columns together. Press the seams so they will butt, ie alternate rows left and right, or up and down. Talk to yourself if necessary as you do this to remind yourself of the plan.
Alternatively, take first and second columns and sew vertically, top block col 1 to top block col 2, don't cut them off, chain piece the blocks below in pairs to the end of the column, then without cutting the threads, stitch them horizontally, butting the seams eg left for col 1, right for col 2. Repeat with next 2 columns, remembering which way to put the seams, until you have sewn all the columns into pairs. If you have an odd number, join that one horizontally. Then join the pairs together, remembering to butt the seams the way they are going already. Add the odd one last. You can press as you go, or leave it all till you've finished. Pinning at the seam will help avoid 'flipped' seam allowances.