Before sending the board out for fabrication, do a final check: Are all the parts in stock? Do the part number match? (design vs stock) Print the board out on paper and do a sanity check that the actual parts fit the board.
Build a mock board by applying the paper copy of the layout to a piece of empty PCB using double-stick tape. Then apply another layer of double-stick tape to the top of the paper to hold the parts in place. Manually place all the parts that are in stock on the mockup to catch any clearance problems or mismatches between the pad patterns and the actual parts.
If everything looks good, look again. Once the layout is submitted to the board house, any change whatsoever means soldering blue wires, cutting traces with an Xacto knife, or throwing the boards in the trash.